Continuity mistake: When Rodney is sitting on the chair and starts eating crisps, you can see that he is sitting on a cushion. It is gone by the time he gets up.
Continuity mistake: When Del asks Lisa how her mum is, he is just about to sit down but in the next shot, he is sat down.
Continuity mistake: When Del & Rodney are talking to Andy on the hill just before Del goes hang-gliding, look at the first shot of Andy. Over his shoulder, the Trotter van is in full view. The shot then turns to Del & Rodney and when it goes back to Andy, there is no van.
Chosen answer: An apparent long string of illnesses.