I dithered and worried about it right up to the last minute (I know, I know... I'm crap!), but the girls were so excited about their 'sleepover' that I'd have felt mean depriving them of it, so off we went.
Me and dh went off on his motorbike (something we haven't really done since before having dd1) and stayed in a nice hotel in the Lake District. We had a lovely walk, went in a boat, zoomed around the country roads a bit, had a drink (... A drink! In a pub!), strolled around Keswick, had a meal, went back to the hotel, had a couple more glasses of wine there... etc!
The whole thing was lovely, and I only wound dh up by saying 'the dds would like it here' and 'I wonder what the dds are up to' about a million times. He only let me ring my wonderful lovely bf, who was looking after them, once - and they were fine (although they did get her up at 5.30 this morning!).
Phew...! I did it! Thanks for encouraging me to go. Next time won't be so hard, and I promise not to stress about it for a month beforehand.