is there no way you can offer lodgings to someone in exchange for a few hours and one night a week of care so you can get a break, ok it is not a long one but a short break each day and a good night sleep once in a while really makes a difference.

talking to your doctor may help as they may know of what support/care is available and may even be able to refer you/your mum.

when my partner was ill and i was his only carer, i bought two very cheap pay as you go mobile phones so if he fell whilst i was out he always had the phone in his pocket to call me for help and i had the other tucked in my bra on vibrate and ring so i could not mistake it for someone elses ringing. it worked really well.

your mum can not expect you to be there 24/7 caring for her, you are young and need a life of your own. is there no way you can get a few hours to yourself during the day by getting her sorted in the morning, handing her lunch and leaving extra drinks etc by her chair/bed and then telling her you are going out for a break and will be back at .... in time to sort her out before supper time. start by leaving her for an hour, then gradually extend the time you are out. even if you only go to a neighbours and rest on their sofa it will be a break in a different environment for a while.

your mum is very lucky to have such a devoted person looking after her but if you continue as you are you will break and need looking after yourself, and who will do that? someone once said to me you have to look after yourself to be able to look after someone else or there will be two people needing looking after.
do not feel guilty by taking 'me time' your mum will be fine, she is capable of being patient and of waiting , so allow her to do these things, explain to her you need a rest and she is only to call you if she really needs you. put the things you usually are requested to get by her so it limits the calls to the essentials like loo trips.