It is not in your head, there is a big probability that bitcoin will go up at anytime, it is in its nature to go up which means that whenever you sell there is a good chance it could go up right afterwards. Of course, there are times when it goes down as well so you could be selling right before it goes down, but that doesn't change the fact that it will not be going up after that too.
So long story short, there is a good chance all of us could sell and it could still go up. What we are having however is the fear of losing too much money so most people end up selling when it is going up to avoid losing money, and when it goes down a lot, the potential of recovering and going up increases even more, hence why it goes up after we sell.
The thing is that you can't always sell "right before" an increase, I understand the point of "bitcoin goes up in the long term" because that's true, but if the person sells "right before" it goes up then there is something fundamentally wrong with that. I am guessing that it takes a bit of time before it goes up and not like 1 hour after they sold but I assume that, I do not know it.
If we take it on face value and say that they always sell 24 hours before it goes up a lot, then we should find out what they do wrong in the trading world, otherwise it doesn't make any sense at all. This is why I have been in trading for a long time, because I know that I would know my strategy and never sell right before a big increase.