I’ve been feeling the past few weeks as though something’s changed in him. He seems more distant, a bit less present or less warm (not really sure which), maybe more professional or clinical, if that makes sense. It’s subtle, but it feels very real to me.

I absolutely HATE those sessions/phases. I completely understand how terrible that feels. I also explained it as being more "professional or clinical" and people just look at me funny like "isn't that T's job?" Well, yes, but it's unusual for our relationship and feels like crap. It most definitely could be something T is going through or perhaps he really is tired or not feeling his best. I call it "Therapist autopilot"...because the usual dynamics and relationship goes out the window and they are literally going through the textbook version of a therapist.

It might be a chicken and egg thing: I’ve been sliding into a depression for some weeks (I fall into one every few months), so maybe I’m perceiving every tic of his brow as a sign of irritation, repulsion and doom because I'm in the pit where I feel irritating, repulsive and doomed. But I’m feeling like what I’ve perceived to be the change in our dynamic is actually what’s making me feel depressed this time. I don’t feel I’ve progressed enough to be able to tolerate a withdrawal of his warmth. Was I just imagining the past dynamic? I feel surreal and scared.

I deal with depression as well and have felt this numerous times. It does not help the problem, that's for sure. Depression creates extra sensitivity because it is a time where we require extra nurturing and empathy. It is also a time where we may already be blaming ourselves for many things, feeling guilty, feeling alone, repulsive, unlovable, etc. So it is so easy to read too far in to facial expressions, responses, vocal tones, and questions. Is it possible he is still the same, but his usual level of warmth is not high enough for how low you are currently feeling? I too have felt like our past dynamic was an illusion or dream that never truly existed. I'm sorry you are experiencing this.

Has anyone had a similar experience? Any advice about how to open up and improve this discussion with him? Any advice about how to get through the pain and depression? It’s another full week until my next session. Might as well be a year.

I say this exact thing to my T all the time! This is when I know I need to increase my visits with her...when I say "it feels like a year goes by for the week to pass", I know I need extra support. Would your T be willing to see you twice week instead? Or at least as needed? Maybe even do one session in person and one phone session? Just a thought worth bringing up with him.
Unfortunately nothing fully alleviates the pain and depression until the situation is resolved. What have you tried telling him already? What has he said to you? When I go through these periods, I write a lot. Actually I write as I am speaking to my T and it helps tremendously. It allows me to make sense of what I'm really feeling and reminds me that our past relationship/dynamic was in fact REAL and I am NOT crazy. I hope this helps or that you are able to find some peace very soon. Feel free to PM me if you don't want to give details on the thread. I'm always willing to help.