I had an experience from the opposite side a few years ago. Our friends Jim and Jane used to be childless, while (at the time) we had two rambunctious toddlers. We often had Jim and Jane over on a Saturday night to watch a movie with us. Now, by the time they arrived, we'd cleaned the house, done a full grocery trip, prepared snacks, plus the 101 other chores and errands associated with running a household and looking after our two girls. Invariably, when Jim and Jane arrived and we asked "how are you?", Jane would say "Oh, I'm soooo tired!"
Now, the thing is, I knew for a fact that Jane's sleep schedule was a bit bizarre - she'd stay up until 3:00 a.m. most nights* watching TV, then she'd sleep until the middle of the afternoon. When she and Jim came to visit us, the most energetic thing she'd done all day was get up and shower - and SHE was tired?
* Yes, most nights. She didn't have a job.