Tapering off

So I’m tapering off bupropion to start Effexor. Bupropion is great for my depression but not as much my anxiety. I was taking 300 and I’m now on 150 and holy shit my chest is so heavy I feel like I can’t breathe. I’ve only been on 150 for two days ..can the switch of medicine effect me that quick or is it psychosomatic? I have a little anxiety already to go to Effexor but when I was on 300 my anxiety has not been this bad. Maybe it’s just my body getting used to the change orrr?? Idk but any advice or like relatable stories would be appreciated:) if you have anything bad to say about like seizures or anything about my safety please don’t mention it bc I’m already way too anxious and I’m following my drs advice. I’m not tapering off on my own.