Illness Benefit/Disability allowance+study for masters

Hi, my current situation is I'm 25 working and unhappy in my job and some areas of my life, recently on antidepressants. I'm thinking of taking a year out to do a masters but seems I am unable to receive any funding from SUSI ect as I just fall outside the parameters.

-Is it possible to quit ones job "due to illness" and go on illness benefit; or does one have to be on illness or disability benefit while remaining with their employer.
-Can one pursue a masters or further education while they are on such benefits.

I've zero experience of claiming state benefits so any advice be much appreciated.

Thanks.