"Drop" is a scientific process that happens to the body after a scene. There are four major chemicals that are released into the body during intense scenes. They are:
Serotonin - the mood stabilizer - Serotonin is released into the body when you practice meditation, spend time in nature, get sun exposure, or exercising and being active.
Dopamine - the reward chemical - Dopamine is released into the body when you celebrate wins, eat a good meal, focus on self care, or complete tasks.
Endorphin - the pain killer - Endorphins are released into the body when you laugh out loud, volunteer or give back, watch a good movie, or when you are exercising and being active.
Oxytocin - the love hormone - You get Oxytocin when you are engaging in physical affection, or giving a compliment.
So now you're enjoying an intense scene with your partner. You are exercising and being active, you are celebrating wins and completing tasks that your partner asks of you. You are saying nice things to one another, and partaking in some big time physical affection. Your body is releasing all of the four chemicals into your body at once.
Masochistic subs usually get the worst kind of drop, because impact is an activity that will light up all four chemicals at once - hard. If subs get enough of these chemicals released into them during a scene, they can appear dazed and drunk, which is a state we refer to as "subspace".
When a sub is drunk on the four chemicals and in subspace, it becomes more important for a dom to pay attention and look after their consent. Subs can get so drunk on the four chemicals that they can lose their ability to adequately defend their own consent, and scenes sometimes have to be halted by watchful dominants who decide their sub is no longer able to defend themselves sufficiently.
Once the scene is over, the body stops being flooded with the four happy chemicals. After the chemical tap gets turned off, people begin to experience drop. There is both sub drop and dom drop, as both parties get these chemicals in varying amounts during scenes.
Drop can be physical, mental, or emotional. Pain finally starts to register, thoughts can get dark and depressive, and hearts can get unsure, and sad. Some people drop harder than others. Drop can come at different times after a scene, and last different lengths for different people. Drop is a chemical reaction that happens to all humans, but is a very individual subjective experience.
The final piece of the puzzle I haven't talked about is aftercare, which is what partners should set about doing for one another after a scene is over, which will help to mitigate drop.
There is your process that leads to drop, and why we in the lifestyle have to be more focused about what it is, and how to resolve it than vanilla people do.
Thanks for the great opportunity to type out this process. I hope this helps.