My dad is in palitive care right now, docs said a week or 2 and he will pass.. I go up their every night and sit next to him.. I sponge his mouth and vacuum anything that he coughs up..and then sit down... I don't say much and he can't really talk. But I do it for him. It hurts to see him like he is so I completely understand what you are saying. You have to do it for them! When someone is going to pass, the only thing you should be concerned about is weather or not you have said everything you always wanted to say before they die. You make them comfortable and just know that they arnt dieing alone and not loved.
Just do what has to be done, you don't get a do over your mother is counting on you.