Wow what amazing replies - sorry I ran off, I had to go out then completely forgot I even posted this!
Your replies have REALLY helped, both in that it's normal to feel slightly shocked, anxious, down and even weirdly slightly embarrassed about turning 50 and in positive memories of 50th years.
I was actually out looking at a couple of venues yesterday (as well as yoga and gym, on a mission to look as good as possible by my birthday. Shallow yes but I don't care!) for a party. My thoughts re party or either everyone or no-one, I find it too stressful to choose just 20 or 30 close friends and family (big family) so would be easier having it for 80-100!
To those saying I should be grateful for turning 50 I wholeheartedly agree. A close relative died at 39 and I think about her pretty much every day even though it was 30 years ago.
Although my health seems to be ok - I am lucky I know that - we have had a bad few years with our kids. One with severe depression, one diagnosed with a serious disorder. But things seem better right now and that's something to celebrate alongside my ancient age.
Oh and the other thing about a party is I get lots of presents! 