Teaching Is Exhausting

We have a new math teacher at our school, replacing one who is on a mysterious "leave of absence."
However, the new guy has been an instant hit at the school: all the girls thing he's hotter than Hades and all the boys think he's cool because he has so many tattoos.  The teachers feel confident that because the fellow only recently left the Marines, he is unlikely to be cowed by obnoxious teens.
He's doing well, even for taking over mid-year as he has.  Of course, he has plenty of support from the rest of the faculty, as we are a school which works together, not against one another.

Friday we celebrated Pi Day with pie before beginning our afternoon meetings, and the following conversation occurred:

New Math Teacher: *enters room and drops onto a chair* I am EXHAUSTED!
All More Experienced Teachers In Room: *knowing laughter*
New:  No, really!  Six months ago, I'd put a 40 lb pack on, hike 10 miles, come home and drink a 6-pack.  I'd be FINE.  Now, I go home after school, drink a glass of milk, and collapse for a nap!  It's UNREAL!
All: *loud laughter*
Science Teacher: It'll get better.
Me: No, it won't, but you'll get used to it!