Like, for instance, when in the grip of a gigantic bout of gastric nastiness and you really, really fancy a Minstrone Cup-A-Soup, don't have one. Reason being, it reproduces itself barely five minutes after you've swallowed the last mouthful and keeps you up all night, not only with increased gastric nastiness but the added bonus of flatulence.
Also, NEVER thank your lucky stars (in your beloved's ear shot) that you're so grateful that "he hasn't had what I've had!" because as sure as Sunday follows Saturday and photographers follow Posh Spice, he will get it, on the very day that you're starting to feel better after ten days. But naturally, "his" bit of it will be nastier, bigger and he'll feel so much worse than you ever did. And he'll be an even bigger drip than you, refusing to - ahem - mop and bleach and generally sanitise everything like what you did. On my first proper day of feeling better (Monday) I spent as much time huddled over the toilet bowl cleaning it as I did when I was in full flow myself.
Plus, NEVER EVER allow your mother-in-law over the threshold when you are feeling less than the full shilling. Added to the fact that my house was not up to standard (cue Amelia standing in the bathroom and bellowing "I thought you said you'd cleaned up here!"), I was "making the house a mess" by my mere presence. My lounging around outfit of tracksuit and T-shirt was deemed inappropriate and I'd feel "so much better" if I put on a nice dress or something. She arrived on Saturday and I spent much of Sunday in tears until she went home.
The first thing I did wrong was "put on a nice dress or something" and headed out to Ruby Blue in Leicester Square for Token Gay Friend Andy's 40th birthday party on Saturday night. David drove Charlie and I over there and warned me against the evils of alcohol on an almost empty stomach - all I'd eaten in the previous four days was toast.
Of course, I was floored by my Woo Woo.
I'll say that again. I was floored by my Woo Woo. Charlie, having drunk a Bramble in three minutes flat, staggered over to the bar to get me "another drink sweets". She returned with a jug of Woo Woo and helped me to demolish it, along with a plate of Cajun Wedges and Stateside Dips. By the time I rang David to come and get me I was beginning to regret everything. Traffic problems meant that he suggested that Charlie and I walk/stagger to Whitehall and he'd pick us up by the Cenotaph. Charlie had got it into her head that he meant Whitechapel and kept talking about Jack the Ripper which set off a gaggle of Japanese tourists who were posing, in the dark, in Trafalgar Square.
I actually think the excessive consumption of alcohol killed off any lingering germs - but don't attempt this yourself.
David did his best to mediate between myself and his mother on Sunday but, when faced with a plateful of greasy pork, overcooked broccoli and rock hard potatoes, I refused point blank to eat it. She then accused me of being a drama queen and insisted I eat "half of it". Now I know how Mac feels when faced with spinach. I said no, she said yes, I suddenly realised I was a 36 year old woman in my own house and in charge of my own destiny so I got up from the table, closely followed by Mac (who came to check I was okay but also to escape his own plate) and then David who spent half an hour stroking my hair as I snuffled into a cushion. She left shortly after that.
But it's not all been bad. I've learnt that, after days of having what my mum would call a "tub down" in front of the bathroom sink because I was completely averse to getting wet because I felt so crap, your first shower is fantastic. I stayed in my first one last Thursday (I know, shocking) for half an hour. Sheer bliss.
And I've also learnt that I have lovely friends - cyber and otherwise - who send me nice emails and bring me lovely books to read and a sister who rings me from the most random of places to ask how I am.
"Darling, I hope you can hear me because I can't hear you but I thought I'd ring whilst waiting for Flavia to finish her flying lesson! I'm at Biggin Hill darling! Kent! Imagine that!"