I agree with Ducky406. It also could be pleurisy. My mother used to get it repeatedly, and that's sort of how it would present. You'd think she'd be coughing but she wasn't. And we usually do know if we've pulled something, but there are times that we do something and not notice that we've hurt ourselves. Definitely go to the ER if your symptoms get worse or don't improve. It can take a little time to feel better, but if you rest it, take your meds, and it doesn't improve even a little, go get it checked in the ER. Better safe than sorry.
In theory you would, but if you're a heavy sleeper maybe not. If the pain gets worse, spreads to your chest, arm or mid back, or if your breathing gets harder go to the ER immediately. I don't want to jump the gun or make you worry, but I lost an uncle because his doctor gave him muscle relaxers instead of noticing he had all the classic signs of a heart attack. So yeah I'm a little paranoid, but I think it's better to be over cautious when it comes to these type of things.