I found this guy that came out of a drainage hole of the pot when I watered it. Small, fast moving.
I took the pic by mobile. It is small so had trouble focusing on it, and it was moving fast, too.
Should I be worried about this insect, or not?
It seems to be a garden centipede - they don't damage plants, they predate other creatures rather than plants. They like to hide in damp places during the day, they need moisture to survive, so possibly it was hiding underneath your plant pot and only ran when it was flooded out. More info here http://www2.fcps.edu/islandcreekes/ecology/garden_centipede.htm
THATS A GOOD GUY!
House centipedes are your allies.