Why do I feel so bloody guilty for going?
Because you're his mum, nelly! Goes with the territory. 
But you should absolutely not feel guilty about it! You will return refreshed and be a lot more use to your son than if you didn't go. You're leaving him in safe hands and you're absolutely doing the right thing.
BTW, I'd better come clean, I'm a bloke - I joined Mumsnet about 6 years ago to ask for advice about my GCs.
And I have to say I'm in awe of the wonderful, strong women I've found on here - and, reading your story on here, I'd put you, nelly, right up there!
Sorry for hijacking your thread, Hush - somehow I don't think you'll mind.
Nice of you to share your focaccia - I tell my students that sharing your home made bread is one of the nicest things you can do with it.
Don't worry about the broken record - that's what this thread is for! 