When any "actual" / physical exposure therapy is too much? That's where I start. Just thinking about XYZ. For just a moment or until I begin to spike. Then back away. Then flirt up to it again, and back away. Then come at it again, and again, and again. Moments, minutes, however long it needs be to only just kiss the edges of anxiety, remain in complete control, and back away.
The biggest trick with THIS one, in my experience, is not "falling in". Aka obsessive thoughts, or ruminating, or racing thoughts, etc.
Once I can think about a thing, and remain calm? Not fall in, go sideways, disassociate, or any other "too much" or out of my control? Then I go onto my more usual step 1.
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I use crowds as an example of exposure therapy an awful lot. My Step 1 there equalled spending a lot of time of rooftops. I would sit on my roof, far far away from the crowd. Above it. Completely outside of it. In the beginning my chest would vice, my skin would slick with sweat, my vision would blur and tunnel. Mad anxiety. Wasn't even in or near the crowd, but a serious spike. It did NOT, however, kick into an actual anxiety attack or panic attack. And the moment I stepped away? My anxiety backed down immediately. So I spent a lot of time on roofs. In the beginning of that, I'd spike, then lean back and feel the wind on my skin, smell the air, watch the sky, completely ignoring the crowd below... Until I felt steady enough to walk... Then I'd go take a shower (always always always wash off the stink of fear and aggression whenever possible!). But that wasn't all I'd do on the roof. Not just spiking hard, but also reading a book, smoking, star watching, drawing. Glancing at the crowd when Inthought about it. Eventually the crowd became both boring (ding ding ding! That's whatcha want!) and kind of oddly fascinating. In part because it no longer causes the anxiety spike, so I could actually see it clearly. Watch the patterns of people as they moved. So I started spending more and more time watching them. Completely chill.
And then I moved down. Found lower buildings, balconies, scaffolding, etc. Mad. Anxiety. Same as when I first started. And same as higher up? The response started to wear off. So then I gradually moved closer and closer to the crowd. Until I was on the same level. But still outside of it. And then on the edges of it. And then in the thick of it.
But where it all started? Step 0? Thinking.
Okay. I f*cking hate people, and it's bloody exhausting, and, and, and, and... I wonder how I might change that? What would make the crowd less everything bad and maybe sorta kinda okay?
I thought a lot about it. It wasn't until I stopped getting furious at even the thought of crowds that I took my ass up on the roof :p And the roof wasn't the first thing I tried. It just happened to be the best / still triggered anxiety, without triggering an anxiety attack.
...
Some things in my life? Are big enough that in order to "start" I can't just "do it". I have to flank it. Thinking. Talking. Normalizing in other ways before I just dive in. LOL And diving in is extremely relative. Diving in wasn't just going and being in the middle of a crowd. It wasn't thinking about them for hours on end, either. Diving in was spending 3 seconds looking at a crowd, and then an hour doing something else, and 3 more seconds.
Crowds? That whole process from the roof onwards? Took me about 6mo. It was reeeeeally slow. But I probably thought about it for around a year ahead of time. It wasn't super pressing, I was back of beyond far far away from crowds most of the time, and avoided them like the plague the rest of the time. It was just a musing. Like a sore spot in my mouth I'd poke at from time to time. Until one day it became "Huh. I wonder...." ;)
Other triggers and stressors I've chipped away at? Have taken as little as a few weeks. They melt away fairly fast. Others are stubborn motherf*ckers & take years. I have no timeline for how long any of them will take, or how long I'll spend on any stage. I just do them, as they annoy me, in little pieces. Chipping away.