Quote Originally Posted by Crake View Post
This is generally what knowledge checks and spellcraft checks are for. Imagine for a moment that a caster is charmed. If they are aware that they have been charmed, wouldn't they instantly attempt to dispel the effect? A normal person might instantly avoid contact with others, to avoid being influenced by the spell. Knowing about after the fact is a deduction, not just an instant awareness of the effect on you.

Negative levels can be similar. If you have no idea what a wight is, and you get hit by one, you'll probably feel weaker, sure, but you won't know WHY. As stated by someone else earlier, it could be a curse, it could be a disease, it could be a poison, who knows. Similarly, a succubus giving you a kiss, you'll feel weak at the knees, but you may quite easily just pass it off as the reaction of being kissed by a beautiful woman. Having knowledge (the planes) or knowledge (religion) is what you use to understand what's happening, or in the case of spells, spellcraft. If you lack these skills that are used to identify things, I don't think it's unreasonable to obfuscate the effects on a character.
This was my thought exactly. I agree that once you gain a negative level a problem would be apparent. I think it makes sense for an applicable knowledge check to determine the exact problem, in this case a negative level. Thanks for the suggestion.