As a stock day trader, what is the most amount of money you have lost in a day?

I think you are asking about “Realized gains” ~$10–15k a couple times.

Most traders mix swing trades and day trades in one trading account and you can see your account balance dip more than “realized losses”, so my swing trades can lose value on days I gain in day trades or vice versa.

I can also gain $$ in swing and day trades and lose in both as well.