Why does Arduino's servo motor go wild?

Hello, developers.

I have a problem with servo motors.

I connected like below.

‘Oculus Rift’ - ‘Unity’ - ‘Uniduino’(Unity’s asset) - ‘Arduino’ - ‘servo motor’

So, I planned as when Oculus moves, Unity checks how it rotated, and Unity transmit it to Arduino in order that servo motor moves.

When I nodded, servo moves correctly.
But when I shook my head vertically, servo goes wild.

When I shake my head to right, it looks like move right, but when some point -I don’t know well- it moves dramatically left to specific point. And it is same when the direction is left.

As I know, servo motors doesn’t reset its rotation automatically, even if the degree is over 180 degree.

How can I fix it?
Thanks for reading!

ps.
I’m so confused so what I wrote is some confusing.

Ah, it’s my problem. My mistyped word made this.
Sorry for irrtating question.