The sun is up, the sky is blue, and your friends want you to come hang out. This would be terrific if you hadn’t just fallen into bed! While many people understand the concept of night shift, and they know you need to sleep, they don’t really get the reality of it.
Explain it to them as clearly as you can. Let them know that they wouldn’t appreciate it if you called them at four A.M. and if they doubt that, offer to call them that night!
Let your friends know that sleeping the during the day is hard for you. Most people are quite diurnal, and unless you are a true night owl, chances are good that you are going to have issues staying asleep when the sun is up. Tell them not to make this harder on you!
If push comes to shove, make yourself unavailable. Tell them you are only to be called under strict emergencies, or even turn off your phone. This can prevent you from needing to stay up at all hours.
Finally, demand respect for your schedule. If your friends want you to be at all functional and friendly, tell them to let you sleep!