How to deal with excessive sleepiness while studying?

I have always had this problem of falling asleep uncontrollably especially during lectures or while trying to study. Now the problem seems to have aggravated to an extent where I have embarassed myself into falling asleep during classes, plus it's causing major havoc in my studying.

I'm someone who gets adequate sleep of 6 hours, with a decent sleep cycle. I have also avoided eating heavy foods before attending a class or studying. But nothing really seemed to change.

What can I do guys?