Pigeon laying next to my garage may have flown into it.

I walked outside this morning and there was a pigeon laying helplessly on the ground and I thought it was dead. Then it started moving it's head. It couldn't really flap it's wings, but when it tried to walk it would just fall over. Should I put it out of it's misery or should I let nature take it's course, after all it is still alive. I am really sad about this situation and have no idea what to do. I am a total animal lover and i feel just terrible. Please help!