Let the altcoin you buy it, you dont have to worry about price down. As long as you are convinced of the altcoin's characteristics, you will surely benefit even though not today.
Just buy it and don't worry, because that price will rise up again and then you leave it so you do not panic if see the price that may will come down again. After a few days I'm sure it will rise again and will surpass the value when you buy it.
Usually I do not get panic when bitcoin prices are falling down but when bitcoin prices are moving up and I will calculate how much profits I'm getting and I start booking profits before price will fall down. This way I have missed many big profit opportunities.