A pal of mine is in your exact position Gene.
He filled out all the paperwork for SW for his Invalidity Pension and even had a medical examination by their medical referee and there were no problems.
Both payments "stand alone" from each other and are not related in any way.
I know that Welfarite has answered your question but I just mention this for reassurance as some of these things can be quite a worry indeed.
Although you are retired on medical grounds I hope that you can make the best of things. You might be a dam sight better off than the rest of us when the provisions of Budget 2010 kick in !