Why Paula? The answer lies in her pediatric history.

Why did Paula get suddenly so sick after suffering a bunch of non life threatening illnesses? 
Before her attack of depressive insanity she had a minor respiratory infection followed by the stomach flu [or the other way around]..anyway you get the picture. 

She was also working in a college which had become overcrowded with students [hundreds  more than the building was supposed to support.] The college was built over a century ago and had humidity and ventilation problems. Mould was found in the bathrooms. The college was located next to an agricultural school with a  cow farm and large corn fields. * The raising of both can cause problems for breathing.

So Paula was also exposed to a variety of pollutants. 

Paula’s paediatric medical history explains why it was all too much for her.  
Paula was born not breathing.  She got stuck for too long in the birth canal of her Mother. Her Mom had  been malnourished as a child and had crooked pelvic bones from childhood Rickets. This is why Paula got stuck and nearly died. 

Paula’s life was saved by modern medicine.  She was resuscitated, she was suctioned [to remove meconium [ingested intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile and water]. Paula was also transfused when resuscitation wasn’t enough.
Paula survived with injuries limiting her ability to breath.  It seems that certain combinations of conditions can cause her breathing to fail.

Hidden injuries to the body due to a difficult birth, illness affecting growth and development and past accidents can take an invisible toll – made visible by measuring the patterns of vital signs at rest or by unusual physical reactions to a bunch of minor illnesses or even by environmental exposures  that trigger unusual responses.

It seems that Paula’s slow breathing at rest and the extra effort it took her to breath, left her more vulnerable to the effects of physical illness when combined to  exposure to pollutants. 

Paula was unable to raise her breathing rate in response to her breathing difficulty and this most likely led to her mental confusion and difficulty speaking.