I think I experience a small amount of sub drop every time I leave my Master. It can last any where between 3 to 6 hours. I feel upset, stressed, withdrawn. It's like I need him to reassure me that its ok. From what I've read, this is perfectly natural. I think its the fall from an adrenaline and endorphine high. As long as its a temporary feeling, I honestly wouldn't worry too much about it. If its a constant feeling... please seek an outlet for help!! No need to be sad!!