tightening/hardening of the male perinium

my husband and i have recently begun exploring the world of prostate massage. we are both comfortable with what we have done thus far (fingertip penetration only as of yet) but are concerned about going any further with it because on the last occasion my husband experienced something a little unusual afterwards in the perimium area. He did have difficulty beginning to urinate at first but was fine once he did (just took a minute)He described the feeling in the perineal area as a tightening or hardening (which we believe to be of the prostate).He also mentioned he felt some pain similar to a cramp-like type of discomfort. There has been no other occurances of this pain or tightening and it lasted approximately 10 minutes. Is this normal to experience? Or is it something we should be concerned about? And should we postpone any further pleasurable activities?