When (if you have) you told your parents you are Athiest, did they accept you?

First off, I would suggest that a threat to take you to a psychiatrist is a scare tactic to force you to assess your beliefs further. If they actually did send you to a psychiatrist, an ethical psychiatrist probably wouldn't even accept you as a client just because you are an Atheist. In fact, a psychiatrist would probably suggest some sort of family approach so that you can sort out these issues as a family, because their reaction is part of a family dynamic, its not about you, as such.
Unless, of course, you are part of a church or religious community that has a "psychiatrist" attached to it. Like one of those ones who "specialises" in "dealing" with gay church members, ie de-gayification. Those kinds of "psychiatrists" are extremely dangerous.

As for if your parents are "over the top"... I would suspect that they are, at the moment, just very shocked and confused. They may not understand what Atheism means, not they are stupid, but Atheism tends to be very misunderstood, especially in religious contexts. I suggest having a relaxed talk with them about what you believe and why you believe it.

As for my story, my parents don't really identify as that strongly as Atheists, but they aren't religious at all, so I never had to come out of the Atheist closet.

My parents have known that I'm atheist for some time now, and they took it alright, they don't care about my religion.

Your parents seem to be overreacting, a belief is just a belief.

I never told them. My sister outed me. >.> Though I tried to hint at it for a while.

I don't think they cared much- they just sort of joked about it. Something about "how did we raise such blasphemous children" and "no Christmas for any of you."

Yes they accept me for who I am :)

of course

I haven't, if I did they would most likely kill me; I'm not even joking.

mine are ok with it for the most part as in they accept it. My mum is agnostic and my dad Jewish I think on part they interpret it as me kinda 'giving up on life' and view it as just a possible stage. But none of this has been vocalised so we can all discuss it and get on fine.
I think its great that you told your parents and are facing the adversity.
And yes it is EXCEEDINGLY over the top. Being sent to a phyc. because of a belief system/religious view is disrespectful on their part (I'm sorry If I am being rude)>