If you slip into a pattern of not waking up at a reasonable time, staying indoors and not exercising, not making attempts to socialise, etc, then it can be quite easy to throw your brain chemistry out of whack and spiral into what is essentially a form of depression.
A job (or a business, partner, family, serious enough hobby, etc) forces you to do all of that, it sets you up with a basic framework, whereas if you are completely free from constraint no-one is going to tell you to get out of bed at 8am, 9am, 10am.... 2pm...
Of course, if you're poor and unable to find work, then you have all of that _on top of_ the financial stresses.