As an English grammar nut and someone who has seen this mistake many times on here and in life...

Nauseated-to feel sick, to feel nausea

I am nauseated means I have nausea,

Nauseous-to cause nausea

I am nauseous means I make people feel nausea or to cause to feel nausea.

So next time you are inclined to say you feel nauseous, remember you are saying you make people want to throw up.

You can say, the taste is nauseous. Nauseous can used to say the something is sickening to think about as well. However, it does not work grammatically to say that you feel so nauseous.

Just thought I'd be all proper and share the 'proper' way to use the terms. Not that people do not know what you really mean when you say 'i feel nauseous' of course, but just a little knowledge.