I think it is one of the following two things, or a combination of both:

1) You have physical causes. I do not know when you had a thorough lab work done, but from what you describe - you WANT to accomplish A, B, and C, but instead succumb to overwhelming fatigue and go to sleep - it could be thyroid dysfunction, it could be one of many types of anemia, it could be vit B-12 deficiency, or maybe you do not have enough vit D3, and maybe a host of other things.

I know that when very low thyroid hits me, I lie like a sack of potatoes on the bed, being physically unable to get up. But no dark thoughts of any kind and no fear of facing the day and no flagging motivation. So it is not depression. It is just low thyroid.

2) You are still sad that you had to give up work and you set expectations of yourself that are too high for the moment. Since you are not working, you expect to be a supermom and a super housekeeper. Well, this is not good to set exceedingly high expectations for yourself and then feel so down by not meeting them instantly that your body goes to sleep, unwilling to face the conflict between the expectations and realistic abilities. If that is the case, subscribe to the thread about positive things you have done today and report small accomplishments. You will see that everybody is doing it - you are not alone. Cooker dinner - check mark; read a book - check mark; took out the trash, walked a dog, paid the bills, caught up on email, etc. It is a very helpful thread - you will see that everyone takes it one day at a time and that everyone (at least the posters on that thread) celebrates small accomplishments viewing them for what they are - accomplishments. Let me see the view count on that thread...