How do you know if you really miss someone?

How do you know when you really miss someone? Is it when you wake up with a start and feel like he's been there all night watching you smile in your sleep? Or is it when you laugh all to yourself over something he said some months ago and still find it funny?
Or how you just can't seem to stop repeating how the way you met was all about coincidence, and how you would never change a thing about it? Or is it when you start to write about the person on your blog, and the words tumble and stall all at the same time?
I think when you are writing about her, she is there in your thoughts...your face would be fluctuating with vivid expression and you do not have any control over it.
Like now...

Happy Birthday Sneh!