I don't understand. 
How can I have a broken night, sleep (badly) for six hours and feel normal and awake the next day...... 
BUT when, last night, I slept well as far as I know, no interruptions, eight hour's sleep, and got up at 7.30 and now feel as tired as can be.
The difference is inexplicable. 

 @bade302b If I were you, I’d go to my practitioner and have my sleep checked. 

https://my.clevelandclinic.org/health/diagnostics/12131-sleep-study-polysomnography