The rules for a forced march still inflict nonlethal damage, as was the case in Pathfinder, but nonlethal damage is no longer tracked independently. It's just regular damage, with a caveat about what happens if it takes you to 0 HP.
If I'm interpreting this correctly, this means a forced march just straight up hurts you, and removing the fatigue only happens if you fully restore the lost HP/stamina?
Also, does this mean DR helps against forced march damage?