I'm so sorry for your dog. It could be that you are having a hard time coping after your dog passed away. Have you talked to anyone about your feelings? Or perhaps it is not one event but several things that are making you so anxious. Do you have any stress at school or in your private life? Are you sleeping enough?
Anxiety rarely passes on its own from my experience. This is why I would suggest you actively try to find solutions. Maybe you could benefit from a few therapy sessions to really intensely deal with the things that have been stressing you out lately. I don't know if you have tried anxiety medication but it might be a good short term solution. Another thing that I would do is check blood levels for any hormonal imbalances or vitamin/mineral deficiencies, because those things can also cause anxiety symptoms. I was also told Chi Gong is supposed to help to calm down. Take vitamin supplements (especially B Vitamins and omega 3) and also if you haven't tried yet, you could try some natural remedies such as kava or valerian. I hope you feel better soon. Take care