I'm stuck in the opposite situation right now. I spent my whole life being skinny-fit. That's thanks to undiagnosed ADHD, which kept me bursting at the seams with energy 24/7. I was always running everywhere, biking, canoeing, hiking, doing martial arts and gymnastics, climbing trees, buildings, etc. I had a natural 8-pack without ever going to the gym. I used to get lots of attention and compliments, and I would turn heads in public pretty frequently.
I never had a big head about my looks growing up. I never really noticed I was all that attractive, I just thought I was "normal." It wasn't until I started losing it that it really hit me.
I broke my leg in my late 20s. Motorcycle accident. It was pretty bad, and my job at the time (US military) rushed me to get back to work and back into the gym ASAP, which meant it didn't heal well. I've basically had leg pain ever since, which has severely restricted my physical activity and almost got me kicked out of the military. Both my legs were compromised; I spent several years walking with a cane before knee surgery finally got me back on my feet unassisted. But I'm still dealing with non-stop aches and pains.
Adding to that... I fell down the stairs in my 30s and messed up my back, so now I basically hurt all the time every time I try to move anywhere. I'm 100% Permanent & Total disabled, according to the VA. I can still walk normally and I don't look disabled if you meet me. But I'm basically in minor pain all the time, just from existing.
As a consequence, exercising has become an extreme challenge and I found myself gaining weight over the years of inactivity. I'm already 75 lbs heavier than my target weight and it's really showing in my gut and face. Swimming is pretty much the only exercise I can do with minimal pain, but I hate swimming. So motivating me to go to the pool has been near impossible and I'm just packing on the pounds now.
I've noticed that people don't give me much attention anymore. I haven't turned heads in public in almost a decade now and people don't go out of their way to help me anymore. Folks are more blunt and rude with me, which hurts because I've spent my life trying to foster positive and uplifting communication with everyone I meet.
Also, at 42 years old, I'm finally starting to show my age. On top of the weight gain, my hair is turning gray and receding, and I'm growing large quantities of unsightly hair everywhere else. People treat me like a tired old man now, not a young fit man. I'm having to come to terms with the fact that, even if I do get back in shape somehow, I'll never truly be attractive again. Now that I'm aware of what I once had, it's already gone. I dunno, maybe that's just part of my midlife crisis, but it's been one of my bigger struggles in recent years, having to adjust to a new me who doesn't reflect the me I see myself as. I feel trapped in an ugly body with weights tied to every limb. Every little bit of movement is a painful struggle and it's frustrating.