Liar Liar

I seem to have begun a strange habit recently of...lying!!! Not horrible lies, but really stupid lies!
The other day, everyone in my house went up to the top floor to see the guy's new hatch and roof garden. So far so good. eveyone goes up the ladder - and suddenly I freeze halfway up! I'm not scared of heights, but i do have a thing about ladders, especially getting down onto one. So I made my excuses and said I had a terrible fear of heights (a lie). So of course this all backfired when everyone swooped around me to check I was okay, and asked tons of questions about my fear of heights ('it's been all my life') etc... Oh dear... I thought it was never gonna end.
And then just this morning, I was a the dentists and it happened again. Lies! You see, I have problems with my gums, and they'd got into a bit of a state again, and I was a bit embarrassed about them, so I just said 'Oh i'm sorry, I went travelling for a while, and you know what it's like when you travel...' (a lie). But obviously I didn't expect the dentist to ask me where I went to ('Egypt'?!!! WEll I'm going to Egypt in a month's time!), what it was like, where my tan was, oh god, again, it was endlesss...
Why do I do it to myself...