2002 Renault Laguna lights keep going up and down when driving along

Sounds like your car has Xenon headlights. These have automatic headlight levelling. This is designed to adjust the level according to how the car is loaded, so add a few passengers and luggage and the back end squats. With other cars the headlights would now point skywards, but the auto levelling on the Laguna should bring them down.

Your problem will be that the sensors which do the adjusting are not working correctly.
Look first at the front left wishbone. (easier if the wheel is removed. You should see that there is a little linkage (about 6cm long) between the wishbone and a small electrical box. Most likely this little linkage has pushed off one end, of if you are unlucky has dropped off altogether.
This little linkage is not available on its own but comes with the electrical box.(which costs about £150). Telephone as many breakers as you like, but most likely this part has already been sold. Fear not. If you have any freinds who are handy with Meccano they could make you a new linkage. The "knobs" which the linkage click on to are plastic and can be removed and replaced with 5mm or 6mm bolts.Note that the new linkage must be able to move.

To work out the required length of linkage...take a look at the rear wishbone (as far as I recall)as there is another one of those boxes with linkage there...
(A quick fix is to make the linkage out of stiff copper wire)

Once you have made and fitted new linkages you may need to reset the head light level. Open the bonnet and look at the top of each headlight. There is hole which a 5mm allen key can fit. Turn the key one way or the other to raise or lower the headlights.