Went the gym at lunch today and when I tried to start the car but nothing

Sounded like it was turning over but not starting.
Tried a few times and gave up and call the AA
Guy turns up 45 mins later, plugs in a volt meter to the battery to check the power and asked me to start it.
Started up no bother. turned it off then on again with no problems.
That fine but now i'm worried.
What happens when I leave work at 5pm is it gonna start ? gonna be worried until its fixed. Anyone else had this problem ?
AA guy said it was probably flooded and could do with a service. but that might not fix it...