Earlier quoted context omitted.
speaking only from my personal experience it can trigger depression, loss of motivation, and a feeling of an "empty head". e.g. place me in front of a window I'd stare out of it for several hours and if you would ask me what I'm thinking about I wouldn't know. Also increased anxiety when the quarantine is over.
You mention smoking weed in another comment. Do you think there may be a connection?
But I strongly agree that smoking for many weeks/months every day could sure trigger a lot of side effects.
Isolation/quarantine right now is very different (I got Internet, and the problem is there is actually too much choice of what I could read, watch or study).
edit: N.N. Taleb talks about his concept of "balancing extremes", I'm very much a believer of this life style.