Not a morning person!

I'm usually awake around 3 am every morning and get up for personal needs and running repairs! 
How ever when greeted by some friendly folk who are then going to work with a "Good Morning'" i usually reply they say with a hrumff!! which they then regard as unfriendly. Really i'm not  awake and will easily fall asleep thereafter and forget the whole incident ,difficult to explain later tho!