Quoting Manda❤Alayna:" <blockquote><b>Quoting EpicThunderCat!:</b>" Benadryl can greatly decrease milk supply ... [snip!] ... my supply. It shouldn't effect it after one night, right?? We have just had a rough few nights and I needed sleep last night."
If you didn't notice a difference by now I am sure you are alright. :]
There are ways to increase your supply back up anyway. I think it's ok.
Remember though, weight loss and lack of wet diapers are the only two indications of low milk supply. So don't scare yourself to much mama <3