There might be, finally, a scientific explanation for that.
"... researchers using powerful new brain imaging technologies are peeling back some of the mystery, revealing how anxiety or stress can rewire the brain, linking centers of emotion and olfactory processing, to make typically benign smells malodorous".
Anxiety interferes with the process of olfactory perceptions and their functions:
"In typical odor processing, it is usually just the olfactory system that gets activated" says professor Wen Li "But when a person becomes anxious, the emotional system becomes part of the olfactory processing stream".
Moreover, continuous exposure to ambient smells while anxious reinforces it, as the person quickly associates the smells with anxiety, and might re-live the anxious feelings simply because of exposure to the ambient odours present at the time the anxiety was triggered.
"We encounter anxiety and as a result we experience the world more negatively. The environment smells bad in the context of anxiety. It can become a vicious cycle, making one more susceptible to a clinical state of anxiety as the effects accumulate. It can potentially lead to a higher level of emotional disturbances with rising ambient sensory stress."
Read the rest of the article "A Shot of Anxiety and the World Stinks: How Stress Can Rewire Brain, Making Benign Smells Malodorous" on Science Daily.