35 year old presents with diffuse weakness.

Answer is below:

There are very large U-waves best seen in precordial leads V2-V5.  U-waves that are this prominent are almost always the result of profound hypokalemia.  The patient had a potassium of 2.2 mEq/L, and has hypokalemic periodic paralysis.

For other cases of hypokalemia, go here: https://drsmithsecgblog.com/search/label/U-waves