So sorry Busylizzie, I know what anxiety and panic attacks are like they can take over your life, specially health anxieties.
To my mind Citalopam is not the correct treatment , you have anxiety not depression, my experience with it was not good, your nervous system is over stimulated and needs to be calmed down.
Citrolopram will dry your mouth out even more so drink plenty of water.
I think HRT (If you are able to with your thyroid meds also not sure about auto immune problems and HRT) it would help more with the moods and panic, and something to calm and help you sleep.
I think the combination of valium and AD can be too much, it would be best to uses the valium on a "need" basis.
This is only my opinion based on my own experiences.
Your anxieties are stemming from your physical problems, and having a hip replacement too ( a big op) has taxed your adrenal glands and probably caused PTSS type symptoms (along with worrying about your mouth problems, brought it to a head) causing the panic attacks. No More Panic is a great site
http://www.nomorepanic.co.uk/forum/ and you will get an insight into panic attacks and anxiety.
Please try not to too stressed as it can effect oral lichen planus( might have been cause by the antibiotics given with hip replacement op)
I have had a blocked salivary gland too, it seem to get worse (gland) and swollen after eating but eventually went away on its own.
Reading my post I have not given much of a solution Busylizzie, but I would advise having a look at the no more panic site.