A Question of Sub-Drop

"I had my first (proper) session with a dom last night. in the past its been just during sex (not even tied up :() . but this was without sex, just teasing and orders. It had me so high! I wish it had lasted longer. I love submitting. but today I'm feeling insecure, low, depressed, anxious... Sub-drop can't come from a more casual first encounter can it? I feel completely out of sorts :(."

I think that sub-drop is a bit different for everyone, and there are lucky people who never seem to experience it at all. But when it happens, it is absolutely no fun.
Sub-drop can be a bit like PMS--it sweeps in and takes over, but it's hard to pinpoint exactly what's wrong. It's just there making you feel crappy, and taking you on an emotional roller-coaster ride that no one wants to be on.

My understanding is that technically, the high comes from a rush of neurochemicals such as dopamine and serotonin. One cannot maintain that high level of those hormones, and when they drop, cortisol and prolactin levels rise, leading to the depressed and "Off" feelings that we call sub-drop.

So yes, I do believe that sub-drop can be a side effect of even the most casual of encounters.

I don't think that it's necessary to just let sub-drop swallow you up though. Everyone has different ways of coping with it depending on their relationships and personal makeup.
When time with the Dominant isn't an option, I would say that the best thing to do about it is be nice to yourself--self aftercare if you will.

Eat chocolate, listen to music you like, take walks in places that make you happy, exercise, read a good book, spend time with friends and family, etc.
Anything that you enjoy and which makes you feel stable and good will help a bit, as will activities, (like exercise) that increase endorphin levels.

I hope this answered your question adequately, and that you start feeling better soon.