Regarding puking, it's my understanding that conditions such as low blood sugar and dehydration can lead to nausea and vomiting. I've had many leg workouts (and a few back workouts) over the years that made me feel nauseous, and I actually did puke after a few workouts here and there (a long time ago), regardless of how long after a meal I waited to go to the gym or how light I ate or whatever.
I noticed this was more common years ago when I did quads, hams, and calves all together (doing an awful lot of intense work in 60-90 minutes) and did not have a particularly good degree of cardiovascular conditioning. I think I was doing too much volume of work (at a very high level of "intensity" or effort) in one session.
In recent years, I've been more focused on overall health and have greatly improved my cardiovascular conditioning. I've also been doing hams and calves in one workout by themselves, followed by quads by themselves several days later. I feel that I need to do a fair amount of volume for each of the three muscle groups, and I simply cannot work all three together sufficiently (in terms of volume and intensity) - so I split leg work into two workouts. Since making these changes, I don't usually feel like I'm gonna puke anymore after even the most demanding workout (quads) of the week. I'm also much bigger and stronger as well.