Pika has been sick before, most of them are with very high fevers and vomitting. Pika gets this one where Pika gets a glare in Pika's right eye, that spreads to take over half of Pika's sight, then Pika gets migraines, and the glare goe away, and the migraines get worse and worse until Pika vomits and is incappable of moving without assistance.
This is just a simple flu though...
Headaches, bis nauseous, tired, runny nose, sometimes a fever of 39-ish C (around the 100 F), in which case, if you do get the fever, you should be doing non-interactive stuff, watching television/series or sleeping, not playing Pokemon3D.