Tonight I just understood why I always had so many SP during my childhood and my all life. 
It seems that some food elements like this one :
img226.imageshack.us/img226/2122 … ing6es.jpg
" made from the natural extract of pure vegetable proteins. Made in China, this sauce features a distinctive flavor and aroma, which adds zest and depth to soups, salads, and vegetables with just a few dashes. An excellent sauce for marinating, stir-frying, and dipping, M****® Seasoning is made naturally without any food preservatives."
…contains a lot of monosodic glutamate, which has a major influence on the melatonine regulation during sleep, and ergo can induce SP. 
I use a lot of that in my food, so that could explain it.