Dear Judy,
Others have given you some sound suggestions. Hence, as my wont, I will ask a few questions to get the situation clarified. Is this the first time that the wrker has slept? If so, have you or the manager tried to find out the reason? It is possible that due to lack of work and boredom, one might have dozed off? For example, I know a friend who dozes off even while listening and saying the prayer loud. If I start reading something, I tend to doze off. That was a huge problem at work, while reading reports. I knew of managers who used to doze off in their rooms.
As you have not given enough information, we all have to ASS-U-ME things and then make suggestions.