Debilitating waiting anxiety

Two days during the week I have a 3 hour gap between classes. Every time without fail I go into waiting mode and freak out for the entire three hours. I can’t get anything done and sometimes I’ll even start physically shaking. It’s been getting worse, and now I get waiting anxiety for the proceeding 24 hours before the day I have the two classes with the gal between them. Im so tired and nothing helps. I have to do this tomorrow and I’m already dreading it. :(