Pizza Horror Story

So I've lost about 35 pounds on compounded sema. I've been following a strict diet. Low-carb, low sugar. I stay within 50-60 carbs a day.

Last night I wanted to celebrate everyone's recent successes, so I bought a couple of pizzas. Mind you, this is the absolute first time I've eaten anything outside your normal range of meat, veggies, whole grain on these meds and my diet.

I ate one slice of pizza at 5 PM. By 10, I had the worst sulfur burps (never had them before) and diarrhea. By 11, I was gasping for air. My stomach felt like I had swallowed a brick that just wouldn't move. I was in and out of consciousness, writhing in pain. I could physically feel the food sitting in my stomach while my organs were just churning at it, trying to digest this alien food. I was ready to vomit but I held it because of the fear of more abdominal cramping. Scale of 1-10, I would give it a solid 8. I was prepared to go to the hospital.

I took 1 antacid and sipped some water. I feel mega dehydrated but if I chug water it will make me nauseous. I finally passed out propped up in bed.

4 hours later and I woke up needing water and a toilet. Stomach pain is gone, I think that was the worst of it.

What on earth could have caused this type of reaction? Is it because I went outside of my diet? My carbs and calories never surpassed my daily limit with 1 slice of pizza. I have no allergies.

Is it because the delay of gastric emptying?

Whatever it is, I'm never doing it again. This medicine is crazy.

Update: Immediately after typing this, I purged what was left, from both ends. Apparently, pizza is a number 1 no go on these meds, and I had no clue.