I don't know what it is but I always feel a wrench when the plane takes off from Ben Gurion - no matter how short the visit. Conversely, I always experience a certain euphoria as the lights of Tel Aviv come into view on the way back and I start to pick out individual landmarks.
I really don't like leaving Israel but work and family dictates that it happens occasionally. This trip in particular involved 2 weddings, my own engagement party to introduce my fiance to everyone and a certain amount of touristy things.
London is expensive. Particularly so with an exchange rate of NIS 8.3 to the pound. My Grandfather z"l used to say that you shouldn't look at the prices when you're on holiday however so we bit the bullet and forked out for various attractions (all of which we booked in advance for - highly recommended to avoid queues!); Buckingham Palace, The London Eye, Madame Tussauds, Chitty Chitty Bang Bang, Romeo and Juliet at The Globe and of course, various shopping trips.
I say "of course" but really it is so expensive that we didn't buy too much; immediately following my Aliyah, visits to the UK would consist of my turning up with a half empty suitcase and hauling around M&S, The Gap et al, returning with said case bulging at the seams. Nowadays I barely bother, one shirt from Next representing my entire clothing purchases for the trip.
I have often noticed that those who have made the move to Israel often see their country of origin through rose coloured spectacles; for me however, other than family and friends, I really don't miss England and always feel far more at home when I'm being honked as I try to change gear by reaching for the window the first time I get in a car on my return!