Just saw this! It has been a little while since you've posted this, but did you ever figure out what was causing him to do it? Poor Traveler!
Harleigh was acting like that (hunched up) a few months ago. Her issue was ongoing and she definitely was acting like herself at all, the vet diagnosed her with a strained back muscle/back spasms and after 2 weeks crate rest (don't know HOW I survived that) she was good to go. Thankfully we haven't had any relapses *knock on wood*
Hopefully Trav is back to new and hasn't had anymore issues! Poor guy