It's horrible the way the bad times are the ones that seem to stick in your mind. When I think of my grandad and my great nan, the only two deaths I've thankfully had to go through, the first images that come to mind are similar to what you just described. Both being completely out of it on drugs and me in a state of fear. I didn't know what to say or do and would just sit there in silence.

There are good times though, and I think we have to make that conscious decision to push the bad memories away and remind ourselves of what we loved about them, what made us smile, what still makes us smile.

That wasn't really your dad, try to remember all the good times and smile that you were lucky to have had him in your life. I know it's hard but maybe it will help