Roller drag lever decided to leave the head. Curious if that was under casual driving or high load/rpm.
At minimum, you'll be pulling / replacing the head(s). Your mechanic can check for lower end damage with a piston height tool. Check for trash in the sump, filter, and in the drained oil.
RealOEM.com * BMW E53 X5 4.4i Valve timing gear, camshaft, inlet
RealOEM.com * BMW E53 X5 4.4i Valve timing gear, camshaft, outlet
Good luck man. You may be able to save the bottom end, and perhaps the other head if you're feeling brave, but really best to just service both heads. Do not start the engine.