I ran down a hill with the guy 25 times yesterday. He said he wanted to do it 30 times, but I imagined he'd tire out or get bored after three runs. He only stopped because his shoe came off and his foot got soaked.
I was thinking of it in workout terms, as it was a lot of work, but he told me it was actually a lot like sledding to him. He liked that the gravity "fastened him up" (by which he means "sped him up").
Then, (I don't know if these events are connected) I slept 12 hours last night. It's nice to not feel sleepy, which I've had a lot of trouble with for the last few weeks, but now I'm worried I won't be able to sleep tonight.
Running down a hill is good is my only conclusion here.