Apart from the vital functions that our automatic nervous system deals with, for example, keeping our heart beating, and lungs breathing, most aspects of being a human, or a member of the animal kingdom in general, require motives.
Remember that time when you simply didn't want to get out of bed. You worked for little remuneration to do another person's bidding, who made a great deal?
Depression is an insidious disease. In the UK it is now over diagnosed, alongside anxiety. One logical reason why those two conditions go hand in hand, is that the increasing deterioration in the all-round functioning of a depressed person, means their social and occupational abilities decline. Any ambitions become increasingly unlikely, and fear and other negative feelings can follow. At an existential level, what was perceived to make up a person's life, not least their social, occupational, and even spiritual aspects, are challenged.
Remaining in bed, is closer to logic, than laziness.