Subspace is an altered state some people enter during an intense scene: floating, detached, dreamy, with pain registering differently and time going strange. It is a real physiological event rather than a figure of speech, driven by adrenaline and endorphins.
What it feels like
Descriptions are consistent. Warmth and heaviness. Difficulty forming words or answering questions. A sense of distance from the body. Pain that would normally be intolerable landing as something else entirely. Some people cannot speak at all, and some cannot remember parts of it afterwards.
Not everybody gets there, and not getting there is not a failure. Some people never do.
Why it is a risk and not a goal
Because someone in deep subspace cannot reliably consent to anything new, cannot judge how much they are taking, and may not use a safe word when they should. They may agree to things they would refuse an hour later, and mean it at the time.
That puts the responsibility on the person running the scene. Watch for it, stop escalating when it appears, and do not treat willingness in that state as agreement. Nothing new gets introduced to someone who has gone under.
The drop afterwards
What goes up comes down. When the chemistry clears, people often feel cold, shaky, tearful or flat, sometimes immediately and sometimes a day or two later. It is common, it is temporary, and it is why aftercare exists.
Dominant drop is the same thing on the other side, and it catches people out because nobody warns them about it.
Topspace
The equivalent for the person running the scene: focused, elevated, slightly outside themselves. It carries its own risk, which is misjudging how hard you are going because you feel sharper than you are.
In a paid booking
An experienced escort who does this work will watch for subspace and manage the session around it, which is part of what the skill actually is. It is also why these bookings run longer than an hour: there has to be room to come down. Fetish and domination escorts covers arranging it.