Bupropion - How to remain calm while having an anxiety attack type thing?

Hi, Kelsey!
Unfortunately new or increased anxiety, nervousness, abnormal dreams, and agitation are common side effects for some people when starting an antidepressant. The good news is that these side effects generally resolve within days to a week or so.
I understand your not wanting to take another medication but if your anxiety persists or you feel it's disabling let your doctor know right away. They may be able to prescribe a ultra short term medication to get you more comfortably through the next few days as your metabolism adjusts to the drug. If you're on a standard initial dose a temporary reduction may also help smooth things out.
Best regards and you should be feeling much better quickly!
Wildcat
PS, You might want to do some deep breathing exercises or the 5 count (count 5 things you see, 4 things you hear, 3 things you smell, etc.) Think of things that take your mind off the situation... a long walk, reading, yoga, meditation, an interesting TV show...