Been on 40mg prozac for 7 months or so, ssris in general for about 8 years. my doctor is switching me to 20mg lexapro (escitalopram). said i could straight switch?

Yes: Yes, that's correct. Those doses are roughly the same and both are significant doses. There should not be withdrawal effects from the switch.

Needs monitoring: Probably ok to just switch, although tapering Prozac and gradually adding Lexapro (escitalopram) is another approach. Bottom line: be sure you are closely monitored for any recurring symptoms of anxiety or depression. You may do well on lower dose Prozac + low dose Lexapro (escitalopram). Only way to tell is frequent clinical assessments by prescribing doctor. I hope this helps. Best wishes.