Nav Mesh Agent - Stuck on ground

Hi,

I have a Nav Mesh Agent that follows a waypoint in a scene with alot of obstacles. The waypoint moves randomly (every time the Agent collides with the waypoint the waypoint moves to new coordinates on the nav mesh). This works fine along the X and Z axis but i would like the Agent (and waypoint) to be able to move along the Y axis too - now its stuck in its Y position. Is this possible when using a nav mesh? What im trying to achieve is a sense of flying.

Kindly Fredrik