Can epididymitis or chronic epididymitis be in remission and can not be diagnosed by testicular ultrasound?

Yes, US is not used to diagnose epididymitis but it can be used to detect the structural abnormality of the urinary tract which can put you at risk for epididymitis.

Epididymitis of any kind is a clinical diagnosis for the epidid can be easily palpated and needs no additional testing. Ch. epidid is rare and other conditions like a cyst can cause pain and be misdiagnosed as ch. epidi. Wear a scrotal support and you will be fine