This is a yoga technique I learned many moons ago.
Lay flat on your back, and make sure as much of the back side of your body contacts the mattress as possible. Close your mouth and breathe slowly through your nostrils. Breathe in slowly until your lungs are full, then breathe out the same way until your lungs empty. Do this about 5 times.
Next, close your right nostril with your finger and breathe in through your left nostril. Breathe out through your left nostril. Close your left nostril and breathe in and out through your right. Close your right nostril, breathe in through your left, then breathe out through your right. Close your left nostril, breathe in through your right, then breathe out through your left.
This relaxes your circulatory system and slows your heart rate. Next, relax your muscles.
Lie flat on you rmattress as you did before. Bend your toes as far as you can, then slowly relax them. Do the same for the arches of your feet. Then your ankles. Then your calves.
Keep doing this method to each muscle group, slowly going up your body. Neck. Face muscles. Then the top of your head. This has the effect of squeezing out the tenseness of your body out the top of your head. Repeat if necessary.
Yes, it sounds like a lot of work, but it only takes about 5-10 minutes. What else have you got to do if you can’t sleep?