How do I overcome that feeling when I see the price of a stock going up and not really going back down?

It's tough to eliminate such feelings if you're looking for short term gains as no one actually knows where the price is heading short term unfortunately. Not recommended but applying technical analysis can reduce such feelings but it doesn't give you any guarantee on any price movements. Please do avoid if you aren't familiar with it.

However, if you're investing in companies long term, truly understanding and believing that it'll offer long term value definitely helps! Basically, having high conviction in your investments. With a strong WHY on why you invest in that particular company, naturally, you wouldn't mind buying at a high price and even FUD won't shake you one bit.

If you are trading, certainly not. If you are investing, remind yourself that the stock is going to get even higher eventually. :)