I'm sorry to hear about your experience with Sertaline. I had the exact same experience 2 years ago and I stopped taking it after a month.
I would give yourself a month to adjust to the medication. Maybe try taking it with or just before food to settle your feelings of sickness.
Give yourself time to rest up while you're feeling rough.
It may be difficult during your trip to London, when is it?
Like you, I had something planned that I really looked forward to (this was 2 years ago when I had just started Sertaline) and I stopped taking it for that period of time...it was awful. Please don't do what I did and stop taking the medication abruptly.
I hope you feel better soon and I'm always here if you want to talk,
Georgia (personless void)
Fighting mental illness one step at a time!