The causes of headache lying down without pain are, low cranial pressure headache, cerebral blood supply insufficiency, tension headache and so on. 1. Low cranial pressure headache: low cranial pressure syndrome caused by insufficient cerebrospinal fluid secretion, excessive leakage or due to lumbar puncture, the cranial pressure will be lower when standing position, which will induce or aggravate the headache and will be relieved after lying down. 2. Insufficient cerebral blood supply: when patients with insufficient cerebral blood supply stand up, due to the effect of gravity, the blood return to the brain is reduced, resulting in a more serious lack of blood to the brain, which will be alleviated when they lie down, and so there is also the phenomenon of headache that does not exist when they lie down. 3. Tension headache: mostly caused by recent excessive workload, fatigue, emotional tension, lack of sleep and other factors, when lying down when the muscles and nerves are flaccid, blood vessel expansion, before the headache caused by blood vessel tension can be slightly relieved, will show the phenomenon of lying down without pain. There are more reasons for headache lying down without pain, the patient should consult the doctor in time to clarify the cause of the disease and timely treatment.