Yup, exactly this. It feels normal to you, because that's how it's always been and no matter what you do, you never actually get a good night's sleep. I dealt with severe obstructive sleep apnea from my late teens to my mid twenties. I have no idea how I was able to study and graduate college, looking back. I got a CPAP and later corrective surgery and it's completely changed my life. Think about how you feel when you get half your normal sleep. Looking back, that's how I felt every single day.