If you do believe that bitcoin will rise again in the future, then, you can invest in this market even intermittently. Even small amount each time you have the opportunity. But remember, you need to spend the amount that you can afford to lose. As you are hoping that one day, it will eventually go up again and earn profits, you need to make sure that you are spending the money that you can very well wait for the right timing. And not hoping everyday that it will be higher than the price you bought it because you need to cash out.
A true believer of bitcoin will not going to hesitate to put any amount of investment even it is small from time to time because they believe that bitcoin was made for a long run and long term hodling. This is already proven and we've also witnessed the ups and downs of market price way back when bitcoin wasn't pricey enough compared today. In my case I am patiently waiting for the rising of bitcoin price again which I believe that it would be possible before this year ends, i believe that there's nothing to be fear of.