Perhaps, instead, feed some input to your brain. Spend your time reading some nice books, memorise some interesting things, learn something fun. Input brings order and clarity to the mind.
Since you have all the time, now that you can't be productive anyway, spend that time creating some order in your mind. Feed your mind with all the stuff it's been lacking.
Aside from that, I find that vitamin D, magnesium, and iron supplements help with quick mental recovery from a cold.
Its possible it was caused by Covid, there are a quite a lot of Long Covid sufferers with just neurological problems.
There’s studies which suggest depression is tied to the immune system, so when your immune system is active it makes you more depressed. Pointing to links like how depressed people get sick less often (? idk if this is true), and how being sick makes people feel down.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7418220/
https://link.springer.com/article/10.1186/s13054-018-2223-6
https://www.cambridge.org/core/journals/the-british-journal-...
There is good evidence now that severe covid (early variants at least) causes atrophy of gray matter in a variety of regions, causing, e.g. loss of smell. Not sure if this is specific to covid however.
As another data point: I got a severe flu a few years ago and felt inexplicably depressed during the illness and a week afterward. Everything in my life was great, so I could tell it was the illness that caused it. It resolved not too long after.
It's very plausible that there is a causal link between inflammation and depression or low oxygen and depression.
There is at least correlation between low oxygen over time and poor mental health, which we see in population studies of high places (suicide rates higher, for example).
I can only speak from my experience in battling (non-COVID) depression that as I have gotten my inflammation under control (better diet, herbal supplements, medication, alternative medicine), my pain and depression have eased significantly.
If you can, attack it from all angles. See a psychiatrist who can find a medication suited to your specific symptoms of depression. A therapist will be important, too. Maybe look into a chiropractor or massage therapist (depression can cause pain). Consider a nutritionist to help you with an anti-inflammation diet. Acupuncture, medical cannabis. I haven’t tried/needed all of these yet, but they’re tools I know I can tap into if needed.
Good luck, feel better.
[1] https://www.psychologytoday.com/us/blog/the-asymmetric-brain...
[2] https://www.nih.gov/news-events/nih-research-matters/long-co...
On the other hand, there are now all kinds of therapies aimed at post-covid recovery. It's not all that bad. You need to get over it even though it's going to take a long time.
(as with treatment for Covid, expect prices to go up in the double digits after a year)
There really is not a lot to look forward to.