u could go with food poisoning matt. symptoms include - headahce, fever, vomitting and diarrhea. medications - dehydrants ( diarrhea and vomitting), paracetemol (fever and headache), and metronidazole ( actual treatement for food poisoning caused by E.coli should give u around 3 day excuse
incase u get asked ok dont bring it up unless u r asked though. if u r asked about the dehydrant ( its a mixture of ions to replenish the ones u lose ok!!) if u forget u can tell him you have been drinking gatorde, or 7 up, or sprite to make up for that.
paracetemol is in Panadol, and motrin both are over the counter medications.
metronidazole is Flagyl ( note name may differ in yr country but in most nations its under that name i,e thats the trade name)