Yep, me too! There is actually a link between high GI and sleepyness; orexin. It's a chemical messenger in the brain, and if you have very little of it, you have narcolepsy. If you have been injected or sprayed with a lot of it, you stay alert without sleep. Oh, and glucose inhibits orexin production!

My personal theory is that I have inherited a low base level of orexin, which makes me react with sleepyness to carbohydrates. I have no idea if this is accurate, though.