so that you can buy bitcoins again if the price is low and sell again if the price is high.. you don't need to be panic if you panic selling your bitcoin you will not making any profit. .and you should always need to have a backup so that if the price continue you can be still make profit for your rest bitcoin..
I do weekly and monthly analysis to deal with this case, I don't really think about bad effects of what happened to bitcoin a few years ago, if bitcoin prices fall in just over a week I remain calm and optimistic prices will rise again, And let's say bitcoin conditions continue to decline more than 3 months then I would also be panicked and start thinking about minimizing losses.