It's very likely safe. The main thing to worry about is if a wire got detached or moved, but I doubt that that would happen just by cracking the socket. However, when you say the bulb fell out, do you mean the whole thing, including the base of the bulb?...because that could be a more serious problem indicating greater damage. If you do have major damage, it would be best if you could throw the breaker for that light until the electrician shows up.

I think a deeper issue is the presence of an open lampholder in a clothes closet.

bad, bad, bad.

Thanks, for your replies. Yes the whole bulb fell out in one piece so evidently I didn't have it screwed in very tight. Think I had better call someone to fix it.
Lois

pharkus makes a great point that I completely zoned out on. While your install may have been legal many years ago, it's not something that's allowed by code anymore because of the fire hazard risk from say, a blanket that is in proximity to the bulb, and the bulb getting turned on accidentally.

I'm glad you're getting an electrician in. Just make sure he puts in an allowed fixture, rather than simply replacing the bulbholder.