How to handle an elder suffering from escalating panic attacks?

Dad died in 2010 and mum's confidence took a dive. She had an isolated panic attack about 3 years ago, but since December 2014 (following a fall and hospitalization) they have become more frequent - several in the past few days. She is on low dose Citalopram which has helped with her general anxiety but done nothing for the PAs. I'm trying to be encouraging, but just don't know what to do when an attack strikes and am a bit concerned I'm making things worse. I was hoping someone else might have handled this.