Yeah, that's a pretty classic effect of IV coke and crack. If you've never experienced it, either you didn't do big enough shots or your coke was horrible.
He said it, as well as various other people...
Opioids are very common to cause nausea and possibly vomiting, but unless you've shot a ridiculous amount, I find that opiate nausea kicks in with a bit of a delay; you certainly shouldn't feel nauseous during the speedball rush. I've had shots of heroin that made me nauseous later (though still not enough to have me purging me innards), but for me it's pretty much a standard effect that I expect when taking large doses of cocaine - that is, injecting it or smoking big, high-purity rocks. I immediately begin to feel sweaty and kind of (sometimes alarmingly) nauseous. Every time I injected blow I felt nauseous, sometimes so strongly that I felt that if I moved up from my seat I would spew all over the floor. A kind of "so good it's almost bad" feeling - and it is really only inches away from bad. But it isn't - it remains good.
When I'm starting a crack session I always try to go for a bellringer on the first hit, but after that I will not smoke for 20-30 minutes because I'm sure another hit would sent me to the bathroom to vomit.
As far as how how long in between shots you should wait.. it's tricky. I mean, ideally you'd wait at least an hour in between shots but when it comes to IV cocaine... the urge to re-dose is super strong and it's incredibly hard not to want to shoot up again immediately after the rush wares off. Just keep in mind, the longer you wait... the better the next rush will be. So use that reasoning to force yourself to wait a little longer in between shots.
If not just for the rush, there's also the harm reduction side to consider - just because the "rush" is over, you're still very much on cocaine - it just feels so meager in comparison to the rush felt minutes ago. With IV and smoked freebase, the peak of the effect is a massive spike, which ends abruptly, and makes the residual effects seem like you're actually at baseline - but taking more at this point is dangerous.
A) Considerable vasoconstriction will make accurately and safely administering following IV shots more difficult
B) Considerable amounts of cocaine remain in your bloodstream for a while, increasing the chance of (POTENTIALLY FATAL, AND OTHERWISE STILL MANIFESTLY UN-COOL) accidental overdose.
C) This kind of use is gonna attach your tolerance to a space shuttle and blast it into orbit.