Loss of levels

I've been working my backside off over the past few days and I've levelled up to 161 on my main character.I just upgraded to my third class and now I've lost all of those levels (All of them!)I know you're going to tell me that it's my fault and I should of upgraded earlier,but I did try and it was telling me that "I can't do that right now" I thought that it was just a glitch and it would get sorted out.I never thought that when I finally got to upgrade that I would lose so many levels! I can't even use my weapon anymore because I don't have the levels to!