just tell them you found the meaning of life and are going into a five day deep spiritual meditation.
Start your own religion, say it's a special day, switch the days as needed and talk about the star formation determining that day.
yeah... may be a developing a new religion, new culture, new language may save you for not going school but that would be of no use as you want to stay home and work on internet... all the best... tell them there is some special assignment given to you and thats to study how people earn money through website on the net....
It's simple, and always works: - Walk down the stairs slowly and quietly. - As you reach the last step take a tumble. - Lie on the floor yelling in pain. - Mommy says "Awww you poor thing, take a day or two off!" (or something similar )
Or just make a concoction that looks like puke, put it in your mouth and spit it all over the bathroom. Used to work for me.