2000 Vauxhall Corsa dashboard randomness???

Hi i've had my car for 5 yrs now and every so often the dashboard will have a moment of boredom and go tits up pretty randomly here's what happens:

Start the engine and the Fog-Light and Main Beam headlight indicator on the dashboard will lightup (fully birght at first and then dim) meanwhile the lights lighting up the dials on the dashboard are very dim (dispite the variable resistor by the door to alter brighteness being full)(consequently in the dark you can't see the dials very well)

Then turn on the headlights and the rev counter and speedometer plummet to zero but mechanically everythings running fine! the fuel gauge will rocket to a full tank and the temperature gauge will hang around 95-98deg.C even though the coolants not even at 40deg.C at startup???

However turn the main lights off and the rev counter and speedo come back??

Also when you drive with this problem the fog light and main beam light indicators on the dashboard will continually flash (and the faster you go the faster they flash)

I've checked for earth faults and fuse faults but nothing everything checks out!

Then randomly over say 2 days of this problem to even upto a week everything suddenly goes back to normal!?? it is really wierd but also a pain in the arse when going through speed cameras at night not having a clue what speed your doing!

Is there a ghost in my car? any ideas?