I noticed last week that our light switch was stiff when turning off the lights. This evening, it's not stiff anymore and requires little effort to turn it on or off. I was also able to move the switch around a bit from side to side, seems to me like it may be loose.
Is this a cause for concern?
Obviously, the switch is failing. The only real danger is that it could produce a poor connection when on and and cause heating within the switch; this is a low probability and I really wouldn't worry about it.
the larger probability is that the switch will fail and you won't the able to turn the light on or off. To avoid running into that issue at an inconvenient time (e.g. it's dark and you cannot turn on the light), I'd go ahead and replace the switch now.
I'm going to make an assumption that you're inexperienced in this, If you want help changing the switch, turn off the circuit at the breaker and unscrew the cover and switch and pull it out of the box without disconnecting any wires. Take some photos and add them to this question. You may see that the wiring is simple enough that you feel confident in doing it yourself immediately. Otherwise, we can help you.
Good luck.
No way to know for sure what the problem is, but something has obviously broken. My guess would be the internal spring; it probably got bound up inside, making it hard to flip the switch, then broke, making it easy. If the spring is in pieces, those pieces may migrate and cause a short somewhere. Or it could be the toggle's pivot that broke. Who knows?
Switches are cheap enough—just replace it.
