I recognize that this tendency is a bit "Valley of the Dolls" in some ways, and is very much frowned upon by industrious, regimented, active, fit, well-adjusted, shiny, happy people the world over.
But I'll be honest: When I had knee surgery last September, I didn't even PRETEND to be upset that I had to do everything from bed for 72 hours. There's just something about cocooning myself into a tiny, compact, Universe-pre-Big-Bang-ball in the dark that makes me feel totally relaxed, safe, and happy.
It goes way beyond simple laziness, (although there's always that, obviously). It's more of a psychological comfort than a physical one. It's not a desire to be unwell or sick or incapacitated in any way at all. It's simply that the world seems smaller and life feels WAY more manageable to me from under a blanket in little to no lighting.
I often question what this says about me, and I'm just happy that my pillow can't answer me back...