I'll share a funny story that's on topic, if you don't mind.
Years and years ago, I worked as a house painter. One of the guys on the crew was a guy who went by the name Mugsy. Mugsy had a bit of a cocaine habit. Since he was a lifelong friend of the boss, this was tolerated. In any case, Mugsy worked off and on.
The boss told me once about what would happen with Mugsy on payday. The boss would pay Mugsy at the end of the day, and then they would all get in the van for the ride home. The boss told me that cocaine is often cut with baking soda, which can act as a laxative. Mugsy would be in the van on the ride home, with a pocket full of money, just dreaming about being able to spend some of that money on cocaine. The boss reasoned that Mugsy's body must have associated money with cocaine with the laxative effect of the baking soda — because every payday, Mugsy would be farting for the entire ride home. He couldn't help himself!
Cocaine is also a stimulant for the digestive system. While not a laxative per se, it can have a similar effect. So Mugsy's symptoms may be more directly related to his body expecting the cocaine.
Is that the (sole) reason? More than one martial arts trainer has told me that if you are definitely about to be involved in a fight -- and you can't run away (number one preference) -- if you have a full bladder you should consciously empty it. Wet trousers are far preferable to having your bladder rupture, so it's a sensible pragmatic (or instinctive) action. I'd imagine there'd be similar benefits in evacuating your bowels.
You experience nausea/vomiting as part of the fight/flight response because digestion, now a low priority, would need blood supply that is more urgently needed by your limbs.
Years and years ago, I worked as a house painter. One of the guys on the crew was a guy who went by the name Mugsy. Mugsy had a bit of a cocaine habit. Since he was a lifelong friend of the boss, this was tolerated. In any case, Mugsy worked off and on.
The boss told me once about what would happen with Mugsy on payday. The boss would pay Mugsy at the end of the day, and then they would all get in the van for the ride home. The boss told me that cocaine is often cut with baking soda, which can act as a laxative. Mugsy would be in the van on the ride home, with a pocket full of money, just dreaming about being able to spend some of that money on cocaine. The boss reasoned that Mugsy's body must have associated money with cocaine with the laxative effect of the baking soda — because every payday, Mugsy would be farting for the entire ride home. He couldn't help himself!