your mind is playing tricks with you, my dear

I had an appointment with my shrink today and he said something that I never really thought of before. I tend to see myself as having two parts that contradicts each other, one of them being the "sick", negative and self-destructing part and the other one being the "healthy", somewhat stable and normal. I told him how I try to defeat and ignore the part of my mind that tells me that I shouldn't gain more because "I look like I'm at a normal weight" and I should get back to 42 kg again, because I know that it's my brain playing tricks with me.
We talked about the preparations of a meeting I have next week about my living situation and that I might be positive about it during the meeting and think it'll work out, but that I eventually might feel like it doesn't matter and I should just move out because I'm not capable of getting better. He then used the words I had used earlier during the appointment, "it's my brain playing tricks with me". That it's not actually anything I think, but just my brain being a fucking bastard.
He is right. When I have those times where I can't get out of bed just to get a glass of water because I think everything is impossible and pointless, they aren't pointless at all. It's my mind - the fucked up part of it - that are trying to convince me that the things are futile and that I'm not worth anything. But it's not my "own" thoughts so to say, it's just the bad part of me that tries to fool me, which sadly it often manages to do pretty well.
Next time I have those days, I'd try to look at it differently. If I can't get out of bed because the self-destructing part tells me that it's meaningless to grocery shopping/take a shower/call someone/etc, I'll try to look at it as if it was the eating disorder that tries to convince me to get lower - that it's all just tricks being played by that part of me. That it's not actually me that thinks that, but "another person". That I have a future, that I'm not a failure and whatnot it would try to tell me.
I know this might seem pretty basic for many who have been/is in the same situation regarding depression, but I've never thought about it like that. That it's actually not me, it's the illness talking. I guess I'm slow or something, but I never really thought of it like that and I feel like something very important has just been revealed. I'm not the self-destructing part.