You sit in your parked car outside the office, hands on the wheel, and notice you can't tell which kind of session that was. Last week your heart was pounding, your thoughts were racing, and you drove home with the radio off because even music felt like too much. Today you talked about the same kind of thing and felt nothing at all. You were calm, almost pleasant, and you're now wondering if you're broken, or if you spent fifty minutes performing a feeling you don't have.

Neither session was a failure. But they probably tell you something useful about a concept that most people never hear about until a therapist mentions it in passing: the window of tolerance.

What the window of tolerance actually is

The term was coined by psychiatrist Dan Siegel in the late 1990s, and it was later built into trauma-focused approaches such as Pat Ogden's sensorimotor psychotherapy. The idea is simple. Each of us has a zone of emotional arousal in which we can feel things, think about them, and stay connected to the person in front of us. Inside that zone, hard material is hard but workable. You can cry and still follow what your therapist says. You can feel anger and still be curious about it.

Step outside the zone and the nervous system changes the rules. There are two directions you can go.

Above the window (hyperarousal). This is the flooded side: racing heart, tight chest, spinning thoughts, irritability, panic, a feeling of being flooded by the memory rather than remembering it. Fight-or-flight energy takes over.

Below the window (hypoarousal). This is the shut-down side: numbness, heaviness, fog, going blank, feeling far away from your own body or from the room. It can look like calm from the outside, but it is closer to the lights going off than to peace.

Two caveats worth stating plainly. The window of tolerance is a clinical model, a useful map rather than a precisely measured brain state, and clinicians use it in somewhat different ways. And it is not a diagnosis. It's a way of noticing where you are.

Why the numb session fools people

The flooded session announces itself. The numb one is sneakier, because it can feel like progress. You talk about something painful in a flat, reasonable voice, you feel no urge to cry, and you leave thinking you've finally gotten past it.

Sometimes that's true. But sometimes the absence of feeling is the nervous system dialing everything down because the material got too close. If you've ever noticed yourself going blank mid-sentence, losing track of what your therapist said, or watching your own story as if it belonged to a stranger, that may be the lower edge of your window.

The tell is usually how it feels afterward. Settled calm tends to feel spacious. Shutdown tends to feel foggy, heavy, or oddly disconnected, and often the tiredness arrives later and harder.

Why change happens inside the window, not outside it

The working logic in many therapies is that you need enough emotional activation to touch the material, and enough steadiness to think about it differently at the same time. Too little activation and nothing is really engaged. Too much and the thinking, reflecting part of you goes offline, so the experience gets relived rather than processed.

This lines up with how emotion regulation works more broadly. Strong emotional arousal narrows attention and makes it harder to reflect, which is why a session that overwhelms you often leaves little usable insight behind, only a bruise. A session that keeps you at the productive edge, uncomfortable but able to think, is where new meaning can actually be attached to an old memory.

There's a quiet permission in this. A good session is not measured by how much you cried. Plenty of effective sessions are quiet and slightly uncomfortable. And an intense session where you were drowning is not necessarily a breakthrough.

Your window moves every day

The window isn't a fixed trait. It's wider on some days and narrower on others. Poor sleep, skipped meals, a fight with a partner, a deadline, being sick, even a hard week of unrelated news can shrink it. Early life experiences and trauma can narrow it too, which is one reason some people hit their edges faster than others. That isn't weakness. It's a nervous system doing what it learned to do.

This helps explain the puzzle in the parked car. The same topic can land completely differently two weeks apart, not because you changed your mind about it, but because you arrived with a different amount of room.

Signs you're near an edge

Your body usually knows before your mind does.

  • Upper edge: a faster heartbeat, shallow breathing, tight jaw or shoulders, words coming out too quickly, the urge to leave the room, thoughts looping.
  • Lower edge: trailing off, losing the thread, feeling heavy or sleepy mid-session, the room seeming far away or flat, answers turning to "I don't know."

Noticing is the whole skill. You don't have to fix anything at the moment you notice, only name it.

Your next moves

  • Add a 0–10 check-in to the start and end of every session. Zero is shut down, 10 is overwhelmed, and around 4–6 is "activated but I can think." Write the numbers down in your phone as you walk out. After a few weeks you'll see your own pattern.
  • Tell your therapist the word, not just the feeling. Say "I'm drifting" or "I'm getting flooded" the moment you notice it. Good therapists can slow down, change topics, or help you ground. They can't adjust to a signal they can't see.
  • Pick one grounding move and practice it on a calm day. Slowing your exhale (for example, in for four, out for six), pressing your feet into the floor, or naming five things you can see. It works better when you've rehearsed it before you need it.
  • Build a ten-minute landing after sessions. Don't go straight into email or a meeting. Walk, drink water, eat something, or sit in the car with the engine off. Treat the transition as part of the session.
  • Track the boring variables. Next to your check-in numbers, note sleep and whether you ate. If your window consistently shrinks on four hours of sleep, that's information you can use when you schedule appointments or decide how hard to push.
  • Write down what you were doing when you left the window. Not a full account of the session. Just the moment, the topic, and which direction you went. It gives you and your therapist a map of where your edges are.

What this changes about how you read your own sessions

Once you see the window, a lot of self-judgment loosens. The flooded session wasn't weakness and the numb one wasn't proof you're cold. Both were your nervous system telling you where the edges are, and edges can be worked with. Therapies built on this idea often aim not to avoid the edges but to widen the window slowly, by approaching the hard material in small enough doses that you stay present for it.

That is hard to do if all you remember afterward is a vague sense of "good" or "bad." The details fade fast, especially the bodily ones, and those are exactly the details that show where your window sits. This is the part Sesh is built for: a private place to jot what you noticed, where you drifted, and what helped you come back, so the next session can start from a real map instead of a mood. If that sounds useful, you can take a look at https://sesh.lumenlabs.works, but a note in your phone and a number from zero to ten is a perfectly good place to start.