I dont know what type of trading you do, but if you are...

I dont know what type of trading you do, but if you are depressed, it probably means you are a fundamentals investor rather than a technical trader.

When money leaves the market, everything falls regardless of relative value.
If you have done your research wisely, when the markets reflate, shares typically bounce back, and those with better fundamentals do so more robustly.

Generally only when you have been pushed beyond your negative sentiment limit is the bottom in and it might be time to buy more.

Conversely when you are ecstatic and love a stock, it is probably time to sell a little of it.

I generally average down when I have a share plummet on me, but that may not be suitable for all shares.