Looks like it was too leggy to me and just fell over, been reaching for more light. Are you giving it any other light besides the window light? Here's what mine look like. Took this picture just for you So I don't think its sick, I just think its too weak/long from not enough light and has been reaching. I would think your other ones will fall over soon too just because they aren't meant to grow upright anyways without support.

Thanks for the info, I'm kind of new to gardening :( should I put them outside? Would that help?

Putting them outside all depends on your weather but they would have to be hardened off first.

All of the plants are very leggy due to stretching too far for too little light. The stems should only be no more than 1/2 that height. Check out the FAQs here on how to grow seedlings indoors. Supplemental lights are required. Window light alone is never sufficient for young seedlings.

Cucumbers are best direct seeded in the garden, not grown with transplants. Not only do they not transplant well much of the time but they grow far too fast for most indoor set-ups to cope with them well enough until they can go to the garden. They tend to stunt if transplanted after the 3-4th true leaf develops.

Dave.

Here is a link that might be useful: Growing from Seed FAQs

As Dave said!

I started a few indoors, though plan to direct seed the 8-10 cucumber plants I plan to have. Just wanted to study their growth process, and they do grow faaaaast. Root bound very quickly.

Hi, I am using a grow light and mine fall over the second I move them out of there. So I dont' know how I can 'harden' them. And they are getting tall, so they will be getting too close to the light soon. I already had a pole bean seedling burn its first leaves on the light because it shot up so fast!

My cucumbers transplanted VERY nicely, too nice... the plants are a foot tall now, so I'm not sure if I need supports for them all now or not? Anytime know what's best to use?