Ok. Firstly, not all your anxiety problems have been caused by IBS. They are inter-related with the two going together. The mind and the body are linked and cannot be separated. There is also the mind/gut link where anxiety plays a part with IBS symptoms.
Also, I have to say that you really need to treat the cause of your IBS rather than just the symptoms. If you just treat the symptoms all the time you will never achieve a cure.
I would not take Immodium if I were you. There are other more natural methods of help out there and I am sure that lots of others on this board will post about the natural methods of control.
You need to look at your diet and cut out things that may affect your IBS. Cut out alcohol, coffee and soda. Try to find more effective ways of dealing with your anxiety and it can also be helpful to take Metamucil. This is a fiber supplement and you GI system needs this to function properly. It is just as good for diarrhea as constipation. Also an probiotic supplement is good. Acidophilis capsules contain the good bacteria that live in the gut and can help to rebalance the bacteria, that are out of balance a lot of the time with IBS and especially in cases of diarrhea. Buy them in a pharmacy or healthfood store and keep them in the fridge. Take them twice daily on an empty stomach.
As I say. You will only achieve cure by treating the cause of your problem rather than the symptoms and try the natural methods first before resorting to drugs.
Immodium should not be taken on a long term basis.