If your alarm doesn't work I always try altering it just a bit with mine I was so used to the exact tone and time it woke me up that I would subconsciously turn it off before I was fully awake, many times resulting in me waking up 1-2 hours after the designated alarm (missed many classes )

Try setting the volume just a bit softer/louder, or even a few minutes earlier/later, that has worked for me in the past. You could even get a new alarm clock I now have 3 for important days when I desperately need to be up.