Sorry I should really put this in the great outdoors but it's so quiet in there.
I have a really scenic walking route near me, should take 5 hours but the footpaths switch at intervals and the map was slightly unclear so I limped out of the other end after getting lost repeatedly after 8 hours solid walking.
Feet have recovered, back hasn't (I assume you'd know if you had a slipped disc?), it doesn't hurt all the time.
I've got some proper walking shoes now and and want to do it more frequently but am a little dubious about the back pain? It's at the base of the spine. Not sure it's worth seeing a doctor about, they'd probably just say to rest it