i lost my dad when i was 16, many many years ago. He passed from brain cancer also.

And i still think about him.

Your range of emotions is typical but know that time and words, especially now, is something you wont ever get back so treat mom with all the kindness you can. Even if she's having a cranky day, tell her a funny memory to make her laugh.

Good luck with your mother and i hope she recovers completely.