There is never a specific amount to describe what "Deep" is when it comes to Bitcoin, because the All Time High you see today could be another deep in either a months or years time, which is one beauty about Bitcoin, of which due to it's usefulness, gives room for more demand, hence, result to an increase in price value. So on that note, the best advice I can give is for people to keep buying the  amount of Bitcoin they know they can always afford to buy without stress of financial instability, while having the mindset to hold for a stipulated long period of time