Ha ha, yeah, classic Sheldon, trying to make a joke even though he doesn't really get them! Catatonia is a form of schizophrenia where a patient is unresponsive, just seems frozen, with a blank stare. It's not a classic coma where you lay in bed asleep. You know how Raj reacts to women, just goes speechless? Sheldon is saying that ladybugs must do the same to him, that they turn him catatonic.