Today's action is one reason I only use stop limit orders and limit. If the market is moving too fast to fill me on entries, then I will just wait for the next trade to come along. If I need to sell at the market on an exit and I don't get the greatest fill, well, at least I am out.
Probably the safest assumption to make is that there won't be liquidity when you most need it. That seems to just be the reality of these markets.