I found IBT to try and fix my sleep issues.
First I built a 6 1/2" wedge out of wood and put it under my mattress. I did this for about two weeks and gave up because the headaches were too severe.
I tried again with two 4" blocks under my headboard bed posts. I am still having headaches, but not as severe as the higher incline. I wake up with the headaches and back pain. The back pain goes away after a couple of hours. The headaches, not so much.
First two weeks can be problematic, because body is undergoing a detox. This means that more salts are excreted in the urine, which in turn pulls more water from the body. I suspect your getting a little dehydrated and drinking more water to rectify this problem is advised.
After two weeks, you should start to improve, but please have your blood pressure measured to determine whether or not it improves.
Starting at the lower elevation is advised. Some are ok with inclining 15 cm others find it too much too soon.
Gravity, Learn to live with it, because you can't live without it!