I'm also on Tykerb since April 2012 (brain lesion found after fainting 1cm cerebellum). Not on tamoxifin anymore since my cancer came back in March 2012, was switched to Arimidex (anastrozole).
I get light-headed at times when I take my tykerb, because its taken on an empty stomach (5 pills/day) and have to wait one hour before eating.
I have to start paying very close attention now to any differences I experience, because my brain tumor has a slight increase and have to report any differences, because it could be an issue with more mets.
Read my story when you get a minute. Take Care and hope this helps you.