The Mustard type is often subject to deep gloom or depression for no good reason. A dark cloud will descend on them for reasons unknown and can lift as suddenly as it comes, and then occur all over again.
I believe the type of people who suffer from this are empaths (one who picks up on others feelings and emotions), who are picking up emotions from those around them, and taking those feelings on as their own. Mustard provides protection and relief.
For Empaths:
Mustard is the remedy for gloom with no apparent reason or warning. It's like you suddenly are surrounded in a dark cloud and there is no rational basis for it. You may feel melancholy or have the 'blues', where nothing is actually wrong, but you feel very depressed.
It should be noted that it's also possible that they are under attack from a negative presense around them.