Hi Pixiedust1
Yes, it seems your dad is scared out of his mind (hardly surprising) and maybe as he can't control what's happening to his wife, he's trying to control other aspects of his life and that includes you - it's also not unusual for parents to rather assume that their children will just step in, drop everything and do the caring especially if the child lives with them (not a criticism, just an observation - my dad was a strange mixture; said it was he and mum against the world, but left everything to me when I was around)
Have you applied for Carer's Allowance (if your mum receives AA and you care 5 hours a day, you qualify)? Built into that is the expectation that carers will take time away from caring - I didn't realise this and cared for my dad for over a year without a week away from him, when I cancelled the CA as dad had gone into a care home, the DWP phone person was very surprised.
Also contact the LA for a carer's assessment - part of that can be to offer YOU chances for respite care for your mum to cover for breaks for you.
So breaks are (notionally) built into the caring system. You might try pointing this out to your dad, to let him see that no-one is required to care every hour of the day -not him, not you. Actually, no adult is legally required to provide the care for another - it's just that we chose to or take on the role due to circumstances.
Also the Attendance Allowance is just that, an allowance to spend on ways to help care for your mum - could be day care, for instance, or a sitter to come to your home. Maybe a couple of days with your mum at a day centre would allow you and your dad some time to do whatever you want for a few hours - he needs a break too, but can't rely on you providing all the cover for him. You can contact your SS/Adult Services to look into this.
Your parents are fortunate to have such an understanding, caring and knowledgeable daughter