Both Uses of
morbid
in
The Great Gatsby
-  "What'll we do with ourselves this afternoon?" cried Daisy, "and the day after that, and the next thirty years?"
 "Don't be morbid," Jordan said.p. 118.9 *morbid = too interested in unpleasant thoughts
- "You're morbid, George," said his friend.
p. 158.7
Definitions:
- 
(1)
(morbid as in: a morbid curiosity) suggesting death and decay; or an unhealthy interest in disturbing thoughts -- such as of death or cruelty
- 
(2)
(morbid as in: morbidly obese) unhealthy or related to disease -- especially of a serious long-term illness
 (The form, morbidity refers to a disease, and form morbidities refers to the number of people affected by a disease.)