The “this feels good” part of the high typically lasts maybe 1-3 hours, after which you smoke more. The actual stimulant effect lasts much, much longer, maybe 12ish hours. That part very heavily depends on the dose size and quality, tolerance and your individual response to it.

Yes, it keeps you from sleeping. At my peak I didn’t really have much use for the concept of separate days since I was normally awake for ~72hrs at a time.

Thanks, that's interesting.

I wonder how much the lack of sleep is what causes the problems, versus other effects of the drug.

Not eating and not sleeping absolutely wrecks your body. Pair that with a general increase in risky behavior (for example, sexually) and you’ve got a recipe for a bad time, eventually.

I’m not aware of meth (or its metabolites) being particularly toxic to the cells in the human body (as opposed to cocaine for example, which is directly cardiotoxic if I remember correctly), my understanding is that the bad stuff tends to be the result of behavior that it induces.