Unaltered Unity cube with Rigidbody goes flying at runtime
I don't know why this is happening because I just did the same thing in another scene the other day and I didn't encounter this issue but...
I added a cube in Unity to the scene I'm working on and put a rigidbody on it. Didn't change any of the settings of the cube and didn't change any of the default rigidbody settings. didn't change the collision settings of the terrain either. When I hit play, the cube disappears and its position and rotation go crazy with its position increasing rapidly into the thousands in either direction and its rotation just jumping around randomly. when I go into scene view with the game still running and double click on the cube to focus on it, nothing happens.
I just uninstalled and reinstalled Unity 5.5 and created the same scenario and the same thing is happening.