Did a urine ultrasound the results were, significant post void residual volume of 278.1. 35 yrs, no other symptoms but tons of anxiety and hypochondria.. nervous it could be sinister.. thanks? was also told the bladder was distended out of 800ml?

That is a significant residual postvoiding residual and a huge amount of urinary retention at your age and raises suspicion of bladder outlet obstruction or a neurogenic bladder problem. Your urologist will have to advise you about causes, treatment and, if advisable, referral to a neurologist.

Yes, you have significant urine retention so I wonder if it caused by prostate enlargement with outlet obstruction or if you suffer any side effect of medication or if you have any neurological issue which can affect the bladder function. Please follow closely with your urologist.