Thinking like a fat person

My family and I went out this past weekend, and when we came out to get back into our car, my husband asked me why I went all the way around the car to get into the front passenger seat, when I could have easily fit through the space between our front bumper and the back bumper of the car in front of us. He laughed at me, and said I was still 'thinking like a fat person'. I realized that it's so true. When I'm going down a narrow hallway at work, I suck my stomach in and press my body to the side with my arm behind me, if I pass a person going the opposite way. I turn sideways to fit into places when very likely I could fit just fine going straight ahead. I avoid sitting anywhere I might have to squeeze between chairs (like some restaurants) because I'm afraid that I won't be able to fit and I will be embarrassed.
This whole 'body dysmorphia' thing is very strange.

I took my teen daughter shopping at Kohl's the other day and every time I caught sight of myself in the mirror, I just wanted to stop and stare. Who is that person? I really don't recognize her. I'm not (or at least I don't think I am) defined by my weight, yet this whole losing weight thing has radically altered my perception of myself. A positive change overall, but it's still a huge mental adjustment.