It's a common trend of regrets coming out when an assest is doing quite well for itself. Most are manipulated and aren't actually event that happens but just attention seekers although that doesn't mean there aren't legit regret out there. If the market is to dumped too you'll still see regret of users not selling at the peak.

You selling at $20k wasn't not that bad if you bought at lesser price, the ideas of trades is to profit so the moment you see profits you should secured it. I understand the price is currently trading above your sell price but don't be too harsh on yourself probably the market will present opportunity for you to re-enter the market below $20k.