Doesn't always happen, but happens often enough that it's a "thing" for me....
The day after an evening flight I wake up and I have sore muscles in my legs, back, neck, etc. I drink tons of water, I get up and walk around/stretch on the flight and yet still, next morning, muscle pain. The weird thing is this never happens with a morning flight, so it has to be something like my body needs a few hours post-flight to get back in shape and if I go to sleep before this happens, the next day I'm sore.
It's not a huge deal, it's not like I can't get out of bed, more like what you'd feel after an intense workout.