Concombres, sounds to me like you're simply talking about taking drugs on an empty stomach!
It's always been a no-no for me, for one actually having something in my stomach if I'm taking an oral dose of something seems to help distribute it into my bloodstream quicker, but also I don't have to deal with those pesky "feel like I'm going to pass out" low blood sugar symptoms.
The tiredness feeling I definitely get on low-dose DMT, actually sometimes feel like I'm literally asleep but it's not a lightheaded everything goes black pass out sort of feeling, more like I'm simply asleep, I'm sorry I know that doesn't make any sense.
0P, the only time of experienced anything close to what you've experienced, the source has been from within myself. Perhaps I indulged in the spice when some part of me is telling me I shouldn't for one reason or another, or I took off the launch pad with some kind of strange trepidation or some stupid thought just catapulted it's self into my brain at lift off. If that may be the cause, only you can answer that.