In a similar way, I typically wake up after 5 hours of sleep. My problem has been identified as “central sleep apnea.” My problem is severe, in that I just stop breathing, awaking in a fight or flight mode, with adrenaline surging thru my body. I have NO collapsing airway nor other blockage cutting off air supply. I just stop breathing, and my oxy level simply drops below minimum levels. The abrupt awakening is hard on my heart, and I recover by deep breathing for several minutes. I can go back to sleep and usually then sleep well and deep for 2-3 hours, awakening feeling good. You might consider wearing oximeter that records your oxy level all night, to record and then see what your oxy level was at the time you awoke. Just sharing my situation which may or may not apply to you. ///