Floppy tomato problem!

[florence]

I have 5 varieties of tomato plants growing on the kitchen windowsill. The are between 5 inches and a foot tall and have been healthy until last week. Some of the leaves have started flopping and dying, this is on all the plants but less obvious on the larger ones. There is no discolouration or any other signs of problems & they haven't been short of water. It think it might be frost damage but they haven't been that cold.
Are they on their way out? Could this be due to them being in a draft or overwatered? I'm not sure if this is terminal for the plants and I need to resow.
Has anyone else come across this?
Thanks for any advice you can give.

[florence]

[goodlife]

Over watering has exactly same effect to plants as does not watering enough..plant goes all droopy.
Try the root ball..tap it out of the pot..how does it feel/look? If the roots and compost look and feel heavy and wet..it might be the reason..and trying to remedy it you need to place the plants on newspaper and hopefully some of the excess soaks away and plants will recover.