This is what it made me think of as well. My first experience with MDMA started out in the grips of anxiety, trembling and feeling multiple uncomfortable symptoms, afraid I had taken too much. I don't think I was able to even stand or walk for several long minutes.

I went on to have a wonderful & memorable experience, feeling closeness & positivity with every human interaction for hours. The worst part after I got over the initial freakout was coming back down. I've heard people talk about such early-stage freakouts happening on other psychedelics, too, but I don't have much experience there.

Serotonin is involved in regulating the digestive system so if you take drugs that act on serotonin like LSD or MDMA symptoms like nausea are quite common.

I did experience motion sickness on LSD so could be related