Yes, you are risking something. For one thing, it takes a while for any dosage change to have an effect, so taking more on one day won't make any positive difference in the way you feel.

For another, while 80 mg of Lexapro may not "seem like very much", it's still more than twice the prescribed dose -- and it's four times the maximum recommended dose! You're already on a high dose of Lexapro, so you are taking risks by taking so much more than your prescribed dose.

If a little is good, a lot may indeed be dangerous. Since anti-depressants take weeks to affect mood, taking more than prescribed isn't going to make any positive difference. You're fortunate that the SSRIs are difficult or impossible to suicide on, but "messing around" like this isn't going to help you at all -- all you can accomplish is screwing yourself up even more. Why do that to yourself?

If you're in such a dark place, call your doctor.