Effexor to Zoloft Switch

Hi ,
I’ve been on Effexor for 15 years with good results ( lowered anxiety levels immensely) until this summer.
My Dr suggested switching ( cross taper) from Effexor to Zoloft over a 4-5 week period.
I’m on week two and feeling terrible- anxiety, nausea, fatigue, dizziness, low mood.
Having an overall tough time.
Have you experienced this? Any suggestions or advice?
Thank you!