You're not imagining it. When you decide to better yourself, you'll be immediately surrounded by people trying to stop you. Action, it seems, offends the inactive.
They'll usually be subtle about it. Offering you foods that work against your nutrition plan, often presented as gifts or treats. Expressing false worry about your supplement usage, your food choices, and the number of days you go to the gym. They'll find plausible reasons for you to cheat on your diet or skip a workout. They'll encourage you to be discouraged. They'll even get mad at you for how your positive choices are affecting their lives.
If anger doesn't work, they'll bribe, they'll mock, and they'll carefully plant seeds of negativity. All because you've decided to be better, to be more.
It's the story of the crabs in the bucket. Put a bunch of crabs in a bucket and some will try to crawl out and avoid becoming dinner. The rest won't try to escape, but they'll reach up and pull the others down.
When you set a new goal, physical or otherwise, you have unintentionally pointed out other people's weaknesses. Their faults and shortcomings. Their inability to plan and lack of desire to express one iota of willpower. They sit around and want. You have royally pissed them off by doing.
Piss them off anyway. Offend them anyway. Crawl out of the bucket and find new friends and better relationships.
Remember, action offends the inactive. And that's their problem, not yours.