Sleeping in the country

I went to my parents' house in the countryside over the weekend, and it seems there is something sleep-inducing about being in fresh air after the noise and pollution that is London.
On Friday I fixed some punctures on my mum's bike, then promptly fell asleep.
On Saturday, I went to town, walked about a bit, went in the shops, then, yes , fell asleep.
On Sunday, I dug a hole in the garden, and broke up some old concrete posts, and then of course I fell asleep.
All this afternoon sleeping didn't seem to have any affect on the evening sleep, so in fact it was 'free sleep'!