Sticky or Problem Keys?

I've recently developed this problem. For some reason, the 'O' on my keyboard has been sticking. Or rather, not sticking but you've got to really punch the key to make anything happen. It's irritating because I'm constantly double-checking my typing to make sure I haven't missed any Os and it wastes my time.

Just any thoughts as to why this started happening? It seems it came on the heels of an update a couple days ago, but that may just be coincidence.

Many thanks in Advance!