There is a 84 year chap on our street and a few of us have asked if he wanted help with the shopping etc. He's always been fiercely independent and mobile, and his response has been basically if he's to stay inside for months, he's got no reason to go on. Its one reason why I seriously worry about isolating the elderly for 3 months, many literally live to get out and have some interaction with society. I've seen first hand the effects of what happen when some do not, and its not nice.
To put this in perspective, if you get cancer and have to undergo chemotherapy, you may well have to isolate for SIX MONTHS or even longer, depending on how aggressively your particular chemo-cocktail disables your immune system.
I am not saying that there won't be people who will suffer depression through self-isolation, just like going through chemo isn't a bowl of laughs. Whether it is better to be a chemo patient sitting indoors seeing everybody else going about their daily lives as normal, or as now knowing that everyone else is in the same boat as you, is debatable. But being told that any infection you get through social contact could kill you, even those that your body would normally shrug off without you noticing, does concentrate the mind somewhat about the necessity of self-isolating.