Yes, is totally normal. Could be teeth, could be a growth spurt, could be fighting an infection, could be any number of things. Just when you think you have got them in some sort of routine, something goes and changes.
I have just admitted on another thread that ds1 didn't sleep through until he was nearly three, so you might not want to take my word on this one (am a co-sleeping hippy type who only ever opened one eye to feed during the night, so night waking didn't bother me much).
9 months is very little. Don't worry, he will be back on track after a while.