since many years i have heavy problems with sleepiness while meditating. The sleepiness starts when i do around 3 hours a day of meditation or more. As soon as i stop the meditation also the sleepiness goes away. What happens is that i start to do noting, things get cloudy and my head drops down... that can happen multiple times in a minute. Its very frustrating, especially on retreat as im "wasting" a lot of retreat time just being in this sleepy state and cant really sustain mindfullness. My guess would be that my brain just thinks its bed time and shuts itself down.

Any suggestions on how to deal with that?  is there a jhana that is known for causing sleepiness?

Here is a list of things i tried without sucess:
- noting the sensations that make up the sleepiness state including my reactions of it
- noting more intense
- sleeping more
- sleeping less
- high doses of coffein
- exercice
- slapping myself in the face ;)
- deep breathing
- cold shower
- standing meditation
- walking meditation ( well it helps a bit for the time i'm walking)