why is my lettuce wilting?

I have grown just a couple of lettuces and the first i pulled up, the second i cut off at the base. Both wilted in what seemed like minutes so wernt very nice to eat. They were lollo rosso.
Can anyone advise of why this would be?
Thanks. x

Were they actually thoroughly crisp before you harvested them?  Good scheme to give the target ones a really good watering the previous evening - if they are stressed before being taken they will indeed flop really rapidly.   Never read it anywhere but it seems to work thus far.