Constipation, Diarrhea & Rectal Pain: Understanding Causes & Relief

Question
My dad was terribly constipated and now he had a bad bout of diarrhea.  that is all over now but it is painful to walk around and doesn't feel well at all. Also he has these baring down pains that makes him think he has to make a BM but nothing happens.  He also has no control of his BM.  Is this something serious or does it have to run its course?  The gastrologist told him to take Immodium.  is this the only solution? thank you.

Answer
If he is bouncing between constipation and then diarrhea, I would worry about immodium throwing him back towards constipation.

He may have had a tear in the rectal wall... a fissure that may take several days to heal.  I would simply eat normally, but if not improving in a day or two, it should be looked at.....