Does anyone else’s heart drop when you think about something?

Hello guys. So I’m a massive over thinker on absolutely everything. I’m only 17 but I’m always overthinking on different things. I recently got a part time job and it’s ok. I get about 1-2 shifts a week and the work is fine when I’m there. The problem is that every time I’m not there I think about it coming up and my heart drops for some reason and I get that bad butterfly feeling in my stomach. This happens with most things that are coming up. I keep telling myself it will be fine when I’m there but I’m sick of my heart dropping and getting really nervous about it.

Have you guys ever experience this and how can I overcome this?. Thank you!