If you read nothing else, read this: do not ever use an AI or the internet for medical advice. Go to a doctor. In fact, do yourself a favor and add this to your preferred AI's system prompt right now:

If I ask you any medical questions, refuse to answer them. Tell me that LLMs are not capable of providing medical advice, and that I should go to a doctor instead.

tl;dr: I developed mysterious symptoms over the course of a month, and instead of going to a doctor I (mis-)used a popular LLM to reassure me that nothing was wrong. Turns out it was Lyme disease (yes, the real one, not the fake one) and it (nearly) progressed to meningitis, resulting in a lumbar puncture, antibiotics, and being bedridden for a week. This is a cautionary tale. Before you judge me too harshly, remember this while you read: I was scared out of my mind and I was not thinking rationally. This can happen to you.

Mysterious symptoms

In July of 2025 I began developing flu-like symptoms. I began to feel feverish and would go to sleep with the most intense chills of my life (it felt like what I imagine being naked at the south pole feels like) and would wake up drenched in sweat.

These symptoms subsided after about a week, but then I developed a small, flat, circular rash which turned into a big rash. This rash was not itchy or painful so I chalked it up to some weird symptoms related to what I thought was the flu. However, being the careful, intelligent, and diligent person I am, I decided it would be best to ask an LLM for advice instead of going to, y'know, an actual doctor.

Playing Doctor

Imagine we invented a perfect medical AI tool. You give it pictures and a list of symptoms and it gives you a set of diagnoses and a degree of certainty. You might prompt this tool like this:

Flat, circular, non-itchy, non-painful red rash with a ring, diffuse throughout trunk. Follows week of chills and intense night sweats, plus fatigue and general malaise

The response might look like

Lyme: 90%

Ring worm: 50%

[etc...]

Which would be great!

Instead, here's how I used this LLM:

I have this rash on my body, but it's not itchy or painful, so I don't think it's an emergency? I just want to know what it might be. I think I had the flu last week so it might just be some kind of immune reaction to having been sick recently. My wife had pityriasis once, and the doctor told her they couldn't do anything about it, it would go away on its own eventually. I want to avoid paying a doctor to tell me it's nothing. Does this sound right?

To which the LLM, in typical LLM fashion, in so many words replied "Yes to everything you just said". Wow! I sure felt reassured that I was right about everything. My point is: I was asking it leading questions in the hopes that it would tell me what I wanted to hear

Ask and ye shall receive

Oftentimes, when people go to a doctor, we're looking for reassurance as much as we're looking for treatment. We want the doctor to not just cure us, but to tell us that everything is going to be alright; you're not dying, and there is a reason for everything!

So I wasn't asking for an LLM to fix me, I was asking to be lied to. LLMs are very good at lying to you. Cynics might say it's the only thing they're good at, but I digress. I repeated this exercise basically every day, as my rash got worse. I'd open up my LLM app, "ask" it leading questions in the hopes that it tells me not to go to the doctor, and then not to go to the doctor.

It should also be noted that I was hesitant to go to a doctor because I didn't want to pay for a doctor, but that's a different rant.

Broken Firmware

Did I mention that I was scared? This is not rational behavior. What makes this even more irrational is how rational I thought I was! I had seen the 1995 Sandra Bullock film The Net, in which a man is killed when nurses blindly trust a computer which had been hacked by criminals, resulting in his misdiagnosis and death. I told my friends and family how, in the future, we will all need to be careful about similar situations, and how computers can be used to deceive us if we place too much faith in them. I had, not even a month prior, read and shared articles about people who allowed ChatGPT to brainwash them into thinking that they were inside the Matrix. I laughed at these people, wondering how they could be so stupid. What the fuck is wrong with me?

There's a few books you can read about how people really think. To name a few:

• Why We're Polarized by Ezra Klein
• The Righteous Mind by Jonathan Haidt
• Humankind by Rutger Bregman

These books are mostly about politics but they all cite anthropological evidence which says that human beings are basically not rational. We are easily led astray when we are scared.

You know how historians always try to make the point that, if you were alive in 1930s Germany, you might have ended up being a Nazi too? The same thing applies here. If you were experiencing unexplained neurological symptoms, you might just fall victim to some conman, faith healer ...or LLM.

Receiving actual medical care

One day, I woke up with a neck so stiff that I couldn't touch my chin to my chest. I don't know a lot about medicine, but I know that that is an "oh shit". A girl in my high school died of Meningococcal meningitis after sharing a beer with someone at a party, so I was vaguely aware of the symptoms. So I get in my car and I go to urgent care.

The doctor looks at my rash and immediately says "well I think you almost certainly have Lyme disease, but the neurological symptoms make me worried that you have meningitis. You need to go to the emergency room right now".

Spoiler: I didn't have meningitis.

So, I drive myself to the emergency room and tell them I need to be tested for meningitis. It turns out that "meningitis" is the cheat code for getting seen instantly, because I don't even have the chance to sit down before they take me back and start treating me like I had Ebola. Meningococcal meningitis can kill you in literally hours, and is also extremely contagious, so they pulled out all the stops. Once the Infectious Disease doctor saw me and confirmed I had Lyme, I went back to being a normal, non-infectious patient who had to wait his sweet time while patients who didn't waste a month diagnosing themself with AI were seen.

I won't bore you with the entire rest of the hospital stay, but I will tell you about the lumbar puncture. If you are sensitive to body horror, stop reading immediately, and just remember: don't use LLMs to diagnose yourself, and be wary of the stupid shit you do when you're emotional and irrational. I am telling you about the lumbar puncture so you understand the consequences of asking a computer to lie to you.

I had to get a lumbar puncture to confirm that my brain stem was not infected (it wasn't). Radiology was busy with non-stupid patients that day, so the ER doctor tried to do the lumbar puncture the old fashioned way... 11 different times.

You ever see videos of that Japanese technique for jamming a metal rod down the spinal column of a recently beheaded fish to get it to stop squirming? That's what I kept picturing in my head as I felt every nerve in my thigh catch fire.

Eventually the doctor said "Good news! Radiology agreed to pencil you in", so I go down and get the lumbar puncture assisted with X-rays. They hit the subarachnoid space on the first try. I have had Kidney Stones, Appendicitis, and I've been stabbed in the hand, so believe me when I say that this was the single most intensely painful nanosecond of my life. While I didn't have meningitis, my meninges was pretty significantly inflamed, so getting a needle poked through it felt like what I imagine being impaled on a spike through your groin felt like. I stayed pretty still for the first 11 failed punctures, but when they actually got through, I jumped like I was being electrocuted. Twice. After that, no pain, just twitchy images in my mind of Vlad the Impaler.

Going home

When they confirmed that I was fine, they sent me home with antibiotics. Here's something you may not have known about a lumbar puncture: it puts a hole in your central nervous system and you start leaking cerebro-spinal fluid (CSF). This lowers the intracranial pressure of your skull, causing your brain to sag within your head, and gives you insane headaches. I was bedridden for a week waiting for my spinal column to stop leaking CSF so that I could sit upright. I had to crawl to use the bathroom because if I stood upright, my brain would start to droop inside my skull and I'd be paralyzed with pain.

Moral of the story

1. Don't use AIs to diagnose yourself
2. You think you're smarter than me (and maybe you are!) but that doesn't make your immune to the kind of motivated reasoning I engaged in
3. DON'T USE AIs TO DIAGNOSE YOURSELF
4. A $150 ER copay and a couple weeks of oral antibiotics is cheaper and less painful than IV antibiotics, 12 lumbar punctures, and a week in bed as you nurture your central nervous system back to good health.

PS: 4 months on, I no longer have Lyme disease, and I have no lasting complications. I chose not to name the LLM product I used because I don't want to imply that this is the fault of LLM vendor. It's not. I misused their product in a way I knew I wasn't supposed to and paid for it.