Yes it is just losing moisture through the leaves and stems thus causing the droop. Is it in shade or sun? You might want to give it a little more shade until it gets used to being outdoors. You can also stake it if you are worried about breakage due to the heavy top parts/leaves. Keep it watered but not too wet. Until it adjusts, it may not be able to take up as much water as it normally would. Another factor of why it is drooping is the stems grew taller and thinner than they normally would due to the less light intesity indoors even if it was in a sunny window. Just needs time to adjust.

I believe it is the latter, growing too tall too fast. I did tie bamboo tomato stakes to the flopping branches to prevent cracking. We'll see how it handles the next few days. I may have to prune it before putting it inground.

It would be wise to prune before transplanting anyway, and then it would bush out. I had a real problem with some of the larger leaved varieties wilting, even in the ground with daily watering. They always wilted in the afternoon, and perked up at night, even in afternoon shade. It's just what they do to conserve water. I was told long ago by a grower not to worry as long as they perked up at night when it got cooler.

Miss floppy (Santa Rosa) has straightened up. I think it was the shock of moving after all. Can't bear to prune it! Next week I'll put it in the ground as it is, some nice compost, fertilizer, and watch it grow. Santa Rosa bloomed all summer long last year.