tcall

Sorry, newbie here. Can't see how to post except as a response.
Just bought an '03 Sentra GXE 500 miles away from home (long story.) Within a few miles, I thought I smelled coolant, but only faintly and not even sure, might have been the Armor All. About 200 miles into trip, going up and down mountains in cruise control at high speed (lots of down shifting for Auto tranny), sudden overheat. This was preceeded by cruise control going out, light blinking for 10 minutes, or so. Cab filled with overheat mist after shut off. Not much leakage at all. Waited for cool engine, read factory manual in glove box. Said something about not using cruise control like I did in mountains. Ran car with heater cranked for 20 min. to gas station. Added about a quart of coolant. Ran car normally, with more caution re. cruise control. Still think I smell coolant. None in oil that I can see, no oil in coolant that I can see. No more troubles over last 250 miles.
Head gasket leaking only slightly till coolant is low enough to overheat?
It's weird to me that it was a sudden overheat.
Maybe used car with a head gasket sealant repair job and some chunk temporarily blocked thermostat?
Bought from potentially shady used car dealer.