Back when I first started taking amphetamines, they wrecked my immune system. I'm not talking like, suppression... they almost fucking assassinated it. This was pharmaceutical amphetamine, by the way, so presumably pure (or pure enough anyway).It's entirely possible that it's excellent, pure amphetamine -- and that amphetamine does the same thing to you that it used to do to me. Now my immune system is shockingly good (considering I'm an amphetamine junkie), but it doesn't necessarily imply anything at all about the speed you've got.Also, I often feel like I've suddenly caught a full blown cold when I'm crashing... a little like a mild flu almost. It's really weird, but it happens like half the time. Don't really know why, and it always goes away by the time I've woken up -- little different than your experience, but it may be related somehow, I dunno.