Hi,
I wish I'd asked here sooner about this - the idea only just popped into my head.
I'm having mastoid surgery to remove an advanced cholesteatoma (a build-up of skin cells behind the ear drum) from my left ear tomorrow.
The issue was only discovered in late February this year, though the doctor told me it must have been slowly developing for years as it's now got to the point where it's away at the ear bones and some of the bone-brain barrier. Unfortunately I don't have an exact time for the surgery, though it's likely to be 8am at the earliest. The procedure can take several hours so will probably take up most of the morning.
I was born with a rare genetic condition called Alagille syndrome which affects virtually every part of my body in some way, but especially the heart
and kidney function, which has been getting progressively worse, especially this year, and am worried about how things will turn out. I've noticed Mars and Uranus are passing through the eighth house at around 9.30am and am wondering if this signifies issues.
The mortality rate is very low but the potential (though rare) side effects like brain leakage, facial nerve damage, increased tinnitus and hearing loss frighten me far more than passing on, which would actually be a relief given how difficult my life has been so far. I've included my natal chart below as well as the surgery chart, any advice or input would be greatly appreciated. 
Welcome, FringedViolet! Just looking at your natal, I think you're going to do well. I say this based on the fact you don't have any devastating transits right now, or in the near future.
Basically, you have a Neptune transit so it's not clear. Saturn and Uranus will engage your planets in Fixed signs later this year but while this transit can scare and surprise you, it's mars in it's home sign and Jupiter we're talking about. I just don't see anything that concerning as far as your having a bad result.
I am not minimizing what you're facing. I know it's huge but I've had A LOT of surgery and these docs tend to know what they're doing!
If they ask you if you want something for anxiety - take it! Everything you can do to reduce stress going into something like this, is beneficial. Your body has to work to heal. The less stress the more energy it has to put to use for this purpose!
Good luck and please let us know how it goes. 
@elsa Hi Elsa,
Many thanks for this, is was very reassuring. Sorry it's taken so long to get back, I've been feeling very drained these last few weeks.
The surgery itself went okay, though I had was terrible nausea after the anaesthetic. I'm prone to nausea but have never experienced anything that bad before. I have a check up on the 23rd where they remove the dressings inside the ear so hopefully I'll know more about how things are progressing. The ear was very sore for the first week or so but it's gradually getting better; the most annoying side effect so far is that I can hear my heartbeat almost constantly in my left ear, though it's not very loud most of the time.
@fringedviolet I'm glad you came through ok! Nausea - Neptune - like being seasick. Hang in there!