Take a warm bath and stretch out your back and legs during/afterwards.
Now lie down on your bed-on your back-and then flip your feet over your head so your cock is above your face. Pull your cock to your mouth by pulling your ass towards your face.
If your bed is against a wall, position yourself so your feet are against the wall. This will allow you to push with your feet as well as your arms.
Don't hurt yourself! and make sure to stretch afterwards.