Just want to thank everyone for taking an interest in this thread and also taking the time to post. Lots of helpful comments and supportive PM's that are much appreciated.
A quick update: on a recent trip, the skipper casually asked if I would like to do the crew briefing. "Sure!" I replied, as casually as I could, then headed outside for the walkaround with my stomach in a bit of a knot!
Found myself hyperventilating, but got myself calmed down with some deep breathing and was able to conduct the briefing with no significant outward display of nerves, (I think) although the first few words felt like cotton in my mouth! The FA's were a good bunch though, and a good discussion resulted and at the end I was fairly comfortable leading the conversation. Weird, but the nerves surrounding PA's have completely disappeared now.
I have heard that the best way through anxiety is right through it; ie; take it on directly. As a result, I am going to volunteer to do more of these briefings (I used to be a Captain at the old shop and had no issue with this stuff at all, hence my surprise at my own reaction of late).
I am also not ruling out the fact I may be burned out, as I fly fairly consistent 95-100 hour months, picking up overtime so wifey can stay home with the kids. This has gone on more or less for the last 5 years. I'm hoping an upcoming month off on vacation will yield some answers and refresh me so I can get back to normal! If not, I am starting the hunt for some professional advice.
Many thanks again to all.