Why am I getting bizarre dreams while on pristiq (desvenlafaxine)?

Common. This is one of the common side effects of this medication. If it is bothersome, discuss this with your prescribing doctor.
Side effects. Abnormal dreams are reported as a side effect in 1% to 10% of people who take desvenlafaxine. REF: https://www.drugs.com/sfx/desvenlafaxine-side-effects.html.