Everyone is insecure once in a while. You can be totally okay with yourself on Monday, and on Tuesday you can feel totally messed up. So. In the last couple of years I developed some things I do when I feel bad.
1. Treat yourself!
This could be anything. A trip to the mall, buy yourself something nice, eat something you crave, read a book, take a bath, get yourself a massage, do something that makes you happy on the inside and try to stop focussing on your exterior. It's JUST weight. YOU are still the same. Probably a better version of yourself.
2. Hang out with friends and LAUGH
I can promise you your friends don't care less about your body size and laughing raises the happy hormone serotonin.
3. List all the things you're grateful about
It makes your body size less important and lets you focus on the things that are genuinely important.
4. Deep breathing
This helps me out in SO many situations. When I feel overwhelmed this seems to do the trick to get me out of the "fight or flight" modus, and lets me step back into my body.
5. Get naked!
I know this seems like the most unrealistic, scariest thing I could ever list. But being naked and vulnerable with myself has taught me my body isn't my enemy. Just make sure you don't have any neighbors peeking through the windows.