Probably not as long as you didn;t have sex. But you are walking a dangerous line. Never ever cheat, it is never worth it in the end despite how much you may think it is.
"Sleeping" with another man is generally understood to mean you had sexual relations. If you are really referring to just taking a nap with "another man" then you need to re-evaluate your relationship with the man you are supposed to be "with". Slumbering with another person is an intimate activity. It is likely that you must keep it secret from your partner. That's dishonest and dishonesty is a flimsy basis for a relationship. If you're that comfortable with it then you should be honest with your partner and let him know you like to slumber with someone else. Give him a chance to back out.