Wow bitcoin down, I have to buy it as soon as possible!
Do not waste this opportunity, if you already have bitcoin then buy it again to increase your bitcoin amount.
If you already have Bitcoins, and if more than 20% of your portfolio is made up of Bitcoins, then I would never recommend you to purchase further coins. Because high risk assets should never cross the 20% threshold in ideal cases. Also, you never know whether Bitcoins will go up or down in the future. Already it is facing a lot of competition from alts such as Ethereum, Bitcoin Cash and Ripple.