That's how the market plays you (and all of us, for that matter). At first, you don't believe in something - "I thought it would be even unimaginable to reach 1K" (personally, I didn't expect Bitcoin to break out of the 1-2k range once it got there), and very soon the market fools you, even though, technically speaking, you didn't lose anything (you didn't earn profits but it is not the same as losing). You think that you have learned your lesson hard ("now I changed my mind"), and then the market proceeds to fool you (read, "teach" you) again and again until you change your mind once more (as some already did)
Then rinse, repeat
The mother of all regrets is not selling at 20k