This can have many associations, depending upon the context in the dream. It can, for instance link with being in hospital where you have to wear pyjamas, and so suggest you are dealing with an issue that needs healing or transforming. See: clothes.
Sometimes this links with sexual feelings, but if so these are usually obvious or suggested in the dream. See Sex
It can be about sleeping and dreaming – linking with the parts of yourself you meet when you drop your guard in sleep; or about intimacy with another person. Do you feel properly dressed in pyjamas? Sometimes a dream shows us still in pyjamas while we are awake and the day is passing and perhaps we are dealing with people. This can suggest we are not properly prepared for what we are doing, or are unclear about how to present ourselves to others.
Useful Questions and Hints:
If this connects with hospital, what is it I am trying to heal or deal with?
Am I uncertain about my direction or how to present myself to others?
What am I feeling or seeing in the dream, and can I translate this into waking situations?