Silly question

This may sound like a silly question it's our first month of TTC and we just BD as I went to stand up I suddenly went all dizzy and had to sit straight back down this has never happened before and it wasn't as if we did it differently or anything.. I also don't know where abouts I am in my cycle as periods only just got back to regular but pretty sure I ovulated about 15 days ago :/ was just wondering why I would have gone dizzy... Thanks