Originally Posted by Gem

I remember in retreat meditating for 12 hours a day for days on end - no headache. I often sit for 90 minutes or 2 hours, and in posture that becomes somewhat uncomfortable, but the basic idea is peace of mind regardless of the body sensations. If a person does happen to get a headache, then they may be at peace with that and after a time it will pass. Of course the retreat, being rigorous and sticking to the pure meditation of mindfulness (as outlined in the satipatthana sutta). Falling asleep is different to meditation, and we sit upright mostly to prevent people nodding off and snoring away in the hall.

In this way of meditation as a formal practice there isn't any effort to silence the mind. One starts with anapanasati, which is 'observe breath'. One will soon recognise just how noisy the mind is, but persist in observing breath. On retreats the mind settles down quite a lot in the first three days. Practitioners become stiller in their physical and mental poise. If we transfer this into say 30 hours, a person practicing for 1/2 hour might expect a fair degree of quietude within 2 or 3 months. Personally I suggest 30 minutes as a bare, bare minimum - at least 45 minutes for sitting practice. I find a one hour session is better and it is that last 15 minutes that really tests the equanimity.

No headaches, so no worries about that.