After an intense BDSM session, many people feel a large drop in their mood - known as dysphoria - which can be a response to the intense physical feelings and emotions that are experienced during a scene. Submissive and Dominant roles can both feel this - they are referred to as sub drop and dom drop, respectively. To accommodate this shift in mood, it’s important to be familiar with aftercare.
Aftercare simply refers to any acts which support play partners through this period of lower mood. Common activities can include cuddling, praise and other forms of affirmation, providing rehydration and food, or anything else that helps the individual in question feel safe and loved. With time, these feelings will pass, and the normal, neutral state of well-being will be restored.
See also:
[0] The Importance of Aftercare
[1] Why What Follows Sex Is at Least as Important as the Sex