i would sell my bitcoins only if the price would start dropping really fast and i would surely know it would never come back to normal
It sounds fair enough to get little loss from the dropping price, thats why holding bitcoin for long time is so risky and can't guarantee us that the price will rise a lot in 5, 10, even 20 years later.
That is not true. The prices are going higher in recent past if you look at the prices. So it will be foolish to wait for next 20 years or so. If you are getting profit in next one year then I think you should sell it and earn profits out of it. Greediness will not help you and you cannot wait for 20 years that prices will reach the sky limit.