Having two cats to look after and who like my company - so I would feel guilty about not spending time with them.
Sometimes - guilt about knowing my partner is out working so hard while I stay at home and currently earn very little money.
Sometimes - work commitments.
Sometimes - the knowledge (from experience) that, although staying in bed all day feels like the one thing I so desperately want to do, I won't feel any better for it. It will actually make me feel worse. So, telling myself that - and giving myself permission so that, even if all I do is sit and watch TV or play with the cats or do some colouring, that is still better for me than laying in bed all day. And sometimes laying in bed all day can seem like I'm feeling better but I'm actually just numbing out and feeling nothing. And feeling nothing isn't really really better, in my book.
Sometimes it's just a determination from somewhere deep within that I won't be beaten and broken and have my life become nothing.
Often, yes, it's finding a sense of purpose, somewhere, somehow, in some way. Whether that's that the cats need me, or that I won't let my partner be working this hard and I'm going to just give in, or that I refuse to be crushed or that I will go for a short walk on a chilly but sunny December morning or that I will do some colouring to try to calm my mind...purpose can just be a conscious choice and commitment to do something - it doesn't have to be the huge issue of life purpose. Finding your life purpose when it doesn't feel you have one can be a pretty overwhelming task. Breaking it down to finding some kind of purpose for today/this next hour can be helpful for me.
I'm sorry you're having a tough time with this. I was only having this conversation with my therapist a few weeks ago. I said that it was so hard to get out of bed in the mornings and that all I wanted to do was stay in bed all day. And she said 'But you are getting out of bed every day...and that's good." I hadn't really thought about that - the fact that I was doing it was kind of passing me by because I was so focused on how hard it was/that I was so tempted to not do it. So, perhaps we all need to congratulate ourselves and each other more for pushing through and getting up. Power to us for that! (Which isn't to say, however, that we should berate ourselves for the times we don't do that!) And I agree with you - it is exhausting.
So, perhaps, ultimately what gets me out of bed each day is a powerful stubbornness that just keeps making me keep on keeping on, even when I want to just collapse in a heap under the duvet.
Gentle hugs to you, if that's ok. I'm sorry you - and so many of us - are struggling with this.