Never ignore something that's "just a cold". A cold is a viral infection of the upper repository system. There are a whole lot of other things that start with very similar symptoms that are much more serious and even a normal everyday cold can progress into other conditions if you are in a weakened state (like exhaustion from overwork).
I can tell you from personal experience. Started out as a "cold", kept ignoring it, it didn't go away and kept getting worse, progressing to a persistent cough and BAM!!! 2 weeks vacation to the local thoracic ward hooked up to 2 drips, coughing up blood from swine flu and pneumonia. My immune response was so bad and the antibiotics were initial so ineffective they tested me for HIV and other immune diseases... I didn't have any I was just that fucked up by the infection.
TLDR: Don't ignore illnesses.