MUGA Scan "lit up" Sentinel Node

 Hello Everyone! 

I'm really hoping one of you might have either experienced something like this or heard of something like this happening to someone else.  I could really use some insight and some calming influence.  I'm pretty much freaking out about a call I received from my Onc today. 

My background is as follows:  I was diagnosed back in March of this year, had a lumpectomy and SNB in April (2cm IDC, no node involvement, Her2+++, ER/PR negative), finished chemo July 22nd, finished Rads 11/12.  Am just starting to get some energy back. 

I went to my BS on Wednesday for a 3 month checkup and had an ultrasound of both breasts.  Everything looked fine and dandy.  On Friday, I went for a Muga Scan.  Today I got a call from my Onc saying that the MUGA came back fine, but the Radioactive Isotope they used to "light up" my heart "lit up" my Sentinal Lymph Node ON THE OPPOSITE SIDE of my cancer.  She's sending me for PET Scan "just to make sure" and needless to say, I'm freaking out.  I'm thinking mets or something really nasty!  

I'm wondering if the Radioactive Isotope just lit up the node just as it lit up the heart and its nothing to worry about OR it's something new.  That's when I think calmly, which I'm having a hell of a time doing right now. 

Has anyone had something like this happen with a MUGA?  Any info or opinions you guys have would be greatly appreciated!!  I posted on the TCH thread in Chemotherapy as well.  I figured perhaps someone getting regular MUGA's might have some insight. 

ETA:  Had a tumor marker test recently as well.  It was perfectly normal.