One of my (high growth) pension pots lost an enormous amount overnight when the EU referendum result came in. We're talk 30% plus, in a few hours. It hasn't recovered from that. Thats on top of the big hit it was taking during the global downturn from about 2008 to 2015ish.
So with high growths come high drops as well and these come round regularly, which is why most companies tend to recommend moving more from risky growth to lower growth but more stable investments in the 10-12yrs leading up to retirement.
30% drop is moderate. It's not considered a 'crash' till it drops 40%, and these can be expected (though not predicted!) on average once every 7-10 years. Some high risk funds have the capability of dropping 90% overnight. People generally don't moan when a fund is going up at 25% a year, but then in year 5 when it drops 90% all hell breaks loose because they haven't understood the risk/reward balance has two sides.
But yes on your second paragraph - with risk comes the potential for reward. More risk in general brings larger reward, and in general as you get closer to retirement you should probably reduce the risk of a big drop unless you are active in managing your investments and know what you're doing.
STEMO's better half has a teachers pension, which isn't invested as such. It's a promise from the govt to pay. It's paid for by govt income (AKA taxes), and if they have to, they'll just put up taxes to pay for it. As such, it's as safe as can be.
A quick check of 3578 funds listed on Trustnet shows "Polar Capital Global Technology I GBP" is currently top of the league table for 5yr returns, coming in at +227%. However it carries a risk rating of 175 (the average fund is sub 100). Bottom of the league is "MFM Junior Oils Trust P Acc" coming in at -56% over 5 years, with a risk rating of 244. Not sure what either of those funds do, and frankly not interested either, but I'd suggest you shouldn't be in either unless you know exactly why.