What is wrong withGrammar and tenses in my resignation letter

[Luke Lee]

I wrote a resignation letter for my boss. But after read it again and again, I just not feel right about my grammar and tenses. Can anyone please tell me what's wrong with this email. Many thanks

I am writing to announce my resignation from Hornet Marketing, effective September 20.My apologies for notifying you by email. I had a very bad headache last week.
A doctor said it's high possible that I had a computer headaches comes from chronic eyestrain and
Neck&Back muscle strain. But we were not certain until we have a proper brain ct scan. Anyway I decide to give myself a long break.
I won't disappear suddenly, I can still help you to interview someone talented, Go through the projects I am working on.

 

[Rover_KE]

I am writing to give notice of my resignation from Hornet Marketing, effective September 20. My apologies for notifying you by email. I had a very bad headache last week.
A doctor said it's highly possible that I have computer headaches caused by chronic eyestrain and
neck and back muscle strain, but he cannot be certain until I have a proper brain CT scan. Anyway I decide to give myself a long break.

I won't disappear suddenly. I can still help you to interview a suitable replacement and acquaint him/her with the projects I am working on.​