What happened to my dog?

My dog is about 12 years old (I know,she's getting up there) and this morning I was taking her on a walk and suddenly she just collapsed, with her legs sprawled out from under her in a very un-dog-like position. She couldn't get up, and I ended up having to call my mom to come pick her up. All day she has just remained in my room, only moving to climb in and out of my closet. At first she didn't have an appetite, but I finally got her to eat some food (turkey meat, almond butter, and wet dog food) along with drinking some water. She lays down with her legs straight out, so it seems as if she is in pain. What happened to her? I think maybe a mini-stroke or a heart attack. If you could help and also post a link to some info, it would help alot. Thanks!