Just the market adjusting and the folks who bet on Britain staying with the EU readjusting. It will straighten out. 

The only way anybody actually will get hosed on this deal is if they are dumb enough to sell during the adjustment period. Once a clear direction is worked out the markets will recover. Same reason why every time there is an election the market fluctuates up and down as investors make investments on the outcomes they wish or want to happen and then half to change them as reality sets in.