Hello
Such type of faintness , after prolong work may be due to these reasons , these include:
1
Hypoglycemia , as due to prolong sitting ,sometimes the level of
glucose decreases , hence there develop faintness . Glucose powder dissolve in water and drink , you will relief.
For diagnosis confirmation get in blood for sugar level.
2 The next reason of such symptoms may be due to
postural hypotension due to sudden wake up . So in routine get in blood pressure examination for confirmation.
3
Anemia may be the another reason . Get in blood for
hemoglobin examination.
However , there are so many other reasons as Mineire's disease , extra exertion etc.
Since this is first time , so ignore it , if recurs then consult a physician and get his opinion.