Blind Spot

I seem to have developed a blind spot in my house as far as my Wifi connection to my laptop is concerned. For the last three months since getting WiFi installed, my laptop has sat on the butcher-block/kitchen island in my kitchen and I have had perfect reception. For the last three or four days, the speed on the internet has been down to a snails pace. I did a test download of Firefox and was only getting 7kb a second, moved about 2 metres right and the speed went up to 250+ kb a second. Now I know that the easy solution is to move my router, but I am more interested as to why I have all of a sudden developed a blind spot. All the other places that I use my laptop are fine (you just don't want to know where I am typing this right now
). Has anyone got any ideas. Nothing has changed in my house, the router is in the same place since day one. No other wireless stuff is being used.
Thanks
Matt

Thanks
Matt