Short answer: 
Cheap alcohol (i.e. produced with no attention to fermentation temps) and overconsumption of alcohol= hangover
Long answer:
Alcohol is metabolized in the body to acetaldehyde. This is the compound mostly responsible for your hangover and a host of other nasty things (i.e. vitamin depletion, cirrhotic liver, accumulation of carcinogens ect...) Acetaldehyde is then converted to another more benign metabolite which eventually makes it to the toilet (in most cases anyway). This conversion of acetaldehyde to its metabolite is the rate limiting step in this process and the amount of acetaldehyde in your body at one time is directly proportional to the size headache you get the next morning. So if the concentration of acetaldehyde exceeds the concentration of the enzyme responsible for its metabolism (acetaldehyde dehydrogenase for all you fellow biochem geeks out there) you get a build up of acetaldehyde. Now fusel alcohols given off by high fermentation temps are more readily converted to acetaldehyde than pure ethenol. So more fusel alcohols wil give higher concentrations of acetaldehyde. However even pure ethanol is converted to acetaldehyde and if you drink enough of it you will accumulate acetaldehyde. Do this repeatedly and you will end up with the other nasty effects stated above. Hence the current medical recomendation to limit your intake to one to two drinks per day. The other confounding factor is genetics. Some peoples enzymes just can't keep up with others.
As to whether belgian yeast strains produce more fusels then others I can only cite my current brew which is JZ's english strong with some oak and vanilla. I let it ferment uncontrolled at room temp (68 nottingham dry yeast). My temp control equipment is currently under the christmas tree. Anyway it has settled down after 4 days and I tasted it today when I checked my gavity. Fusel city! This thing is hot and nasty. I'm sure it will mellow some over the next ten days but it will probably need some significant aging befor its drinkable if it ever will be. Anyway IMHO I don't think the production of fusels is so much yeast strain dependant as it is temperature dependant.
Sorry for the lengthy boring post but I did offer the short answer  
 
 PB