A 5.5% is normal market 'noise', or perhaps at worst correction.
A 40-50% drop is a normal crash, and happens once every 7-10 years on average. The last one was in 2008, which was 8 years ago

Investing in only 6 FTSE100 companies is very high risk - as Sir Humphrey would say a very brave decision. If it works, and you pick a Microsoft/Apple/LinkedIn then you win big. If you pick Northern Rock, Woolworths, BHS, well you know. Most people with small portfolios do it for dividend income - so they're usually in at least one Cancer stick company (BAT/BAR etc), one bank, one supermarket, one food company etc.
There is no way that a normal punter like you or me will be able to out guess the markets. They will already have priced in all the known or likely risks. And if new information becomes available they will react before you even get a sniff of the story.
I don't like individual shares, or the FTSE100 for that reason. If you want to hold FTSE100, then I'd rather hold a tracker fund - these can have charges in the 0.2% p/a region. However, I'd prefer a world wide balanced set of funds, and that includes things like Global small cap, US, China, India etc. These have world wide income, so if a piddling economy like the UK falls over because some nutters decide to Brexit, then yes it'll impact but not nearly as badly as I thing the FTSE will fare.
In short, don't 'invest' more than you can afford to lose, and DYOR.