I’ve not been officially diagnosed with hypnic headaches but feel sure this is what I’ve experienced for years. Typically they occur during the night, waking up with headaches at times severe and occasionally with nausea. What works for me is caffeine - actually I use half-caf. By the third cup of coffee and within an hour, the headache goes away. I’ve also been helped by rinsing my face with cold water? It doesn’t happen every night but approximately 10 times a month or more. I do not sleep well typically.