Vanlafaxine IR vs XR : Effexor

I was on Venlafaxine XR 150MG for almost 7 years (age 15-23). Went off it to try and get pregnant (withdrawals even with tapering were awful), turns out we can't (we are fine with). Im now 31 and my anxiety disorder has turned into an anxiety AND panic disorder and I'm a major hypochondriac. Doc prescribed me Vanlafaxine IR 75mg. I took one dose after dinner and felt horrible nausea. I started to panic a little and my heart was racing. Then I had vomiting and diarrhea all night. I could NOT sleep. Every time I'd fall asleep, I'd wake up immediately gasping, it's like my body was scared I wouldn't wake up. I had high blood pressure the next day. Told my doc and she thinks I had a panic attack. She prescribed me extended release 75mg. Does extended release have less side effects or less severe? My mom take XR 75mg and she says she takes her before bed and is fine. Any advice, words of encouragement or info on the difference between these two would be appreciated. I'm scared to take this XR (despite me taking it for years) because that IR messed me up so bad. Im terrified of serotonin syndrome too. I'm a mess lol