Waiting for a higher price is good idea for some holders ,but if you feel that bitcoin price is in danger or it starts to go down ,then basically you must sell it before it will go down deep.
No, that is panic selling and that is the fastest way to lose money, sell when you get a profit and if you are in the red, then wait until you are not, the
price of bitcoin always recovers relatively fast. Yes correctly said, now a days even in a day there are many ups and downs and in the end of the the day everything comes to the initial position.