I find that when I eat lunch I can feel myself instantly get tired as if a wave passes through me. My face gets a feeling of being sweaty and flushed. Coffee and copious amounts of water help counteract this. Also, it doesn't happen every day with every meal. Very small amounts of food don't cause this. It's as if I eat above a small threshold, then it happens. It makes it hard to work. A short nap would be perfect (but not possible). Is this something to be worried about?