Feeling the writing

I'm sitting in a very public coffee shop while I write--my place of escape, if you'll remember--and realize as I'm writing that I have a very stupid smile pasted on my face. I'm in the middle of penning a happy moment in the story and I feel happy as I write it. I feel what the character is feeling. The patrons don't know this and probably think I look like a doofus. I also cry when I write something sad so it's a good thing I'm not writing one of those scenes today. I spend so much time in the character's head, it's hard not to feel what is happening as I write it. I'm sure this is normal. I remember Fantasia Barrino's fantastic rendition of Summertime and how she really FELT the song to the point of tears. It's good to get involved in what I"m writing, but on the other hand, it means mood swings.