I think it's fine. I certainly wouldn't mind someone sleeping in the lounge, provided that you don't snore or otherwise bother me.

Once, I was so tired (didn't get any sleep the night before) and fell asleep in an Admirals Club. Would've missed my flight if it wasn't for the guy I chatted up at the bar earlier (so he knew I was on the same flight) waking me up. I thanked him profusely.