Berries, it is the worst feeling.
'The call of nature' is the only thing that can get me to move under those circumstances.
Don't be so hard on yourself and accept it rather than fighting it. You know from experience that it will pass. Just think about the next minute, rather than anything long term and overwhelming.
One thing I do that helps is talking myself through things out loud. I give myself instructions out loud when I am getting dressed, etc. or it won't happen. Sounds ridiculous, but it does help. I should mention it takes ages to accomplish anything and I am very easily distracted.
When I have a good day I can function normally. I always say to myself,
"Everything is so easy when you feel well".
So fortunate to have the internet and know that others are going through the same thing. It seems like the only consistent thing is the inconsistency of the mood/energy.
Hope by the time you read this that you are feeling better.
Sending positive energy to you.