Has this happened to you?

Last night the upper part of my legs felt very sore, like I had worked out hours or something. I ignored it (it was more uncomfortable than anything) and went on to bed. This morning when I woke up the felling returned. I have not done anything out of the ordinary that would cause me to be sore like this nor have I exercised more than usual. It is both of my legs and sometimes down to my calf. It feels like I am very sore. It is uncomfortable to stand or stretch but if I'm sitting down then I am ok. Has this happened to anyone before?