Adding a zigzag to a line and getting a helix shape..

I am trying to make a nice looking Sine Wave by drawing a horizontal line with the pen tool and then adding a smooth zigzag to it, but whenever I add it, a helix shape is made. It seems like the effect is affecting the path twice. I can make it look correct by adding trim paths and cutting half of it off, but that is impacting the way I would like to animate it. See image for reference,

Thanks for the help!