Yes, it’s possible. I tried this once with an ex lover. He had his 8 inch penis in my mouth up to about 5 inches for most of the night. It was his suggestion that I try this — i had never even thought about it before, but jumped at the chance.
Initially, it was quite difficult to get to sleep with a big dick buried in my mouth, but after a while, I just got really tired and fell asleep for about three hours. I was woken by his cumming in my mouth while he was still asleep! I swallowed it all down like a good boy and sucked him clean while he moaned softly in his sleep. I got back to sleep about thirty minutes later, but then got woken again about two hours later, to my lover actively grabbing my head and “face fucking” me to his second orgasm, a much larger, more powerful orgasm that I nearly choked on because I could hardly swallow fast enough.
I tried to sleep again afterwards with his penis in my mouth but it was difficult. I think it fell out of my mouth a little later and I slept with his dick on my face. He woke up about an hour later, fresh as a daisy, while I work up so tired, with jaw ache…but with a nice taste of my lover’s orgasm in my mouth.