In your case, the problem is that there wasn't enough liquidity to execute your stop loss. Thus, your order was closed gradually, as counter orders placed by other traders became available. You can avoid this if you set a stop-market rather than a stop-limit.
Stop limit orders never get executed away from the set price. They only get executed at the set price. Worst case scenario if the market was moving so fast and the stop limit order wasn't triggered in time, no execution would have happened and OP would have been left holding a losing position until the price came back up or even get the position liquidated. For OP's case, I am guessing he used the stop order(market) and due to slippage caused by the fast moving market, his position got closed away from the price he wanted thus that huge loss.
Thanks for the replies... Yes this is what happened (i.e "
he used the stop order(market) and due to slippage caused by the fast moving market, his position got closed away from the price he wanted thus that huge loss.")
I assume it must have been a liquidity problem as tvplus006 suggested.... Does this mean it would not have happened if I'd have been trading a bigger coin such as BTC or ETH (due to higher liquidity)? And if that's the case I assume that means Bybit has higher liquidity when trading smaller coins/tokens as this never happened to me when I traded on Bybit? Or, was this just simply 2 very rare occasions when the market dropped alarmingly quickly and I was just extremely unlucky?