I cannot answer how fast your depression can "come on". The power of suggestion is often strong when we read to much on a medical condition we start to feel we must have that illness. I believe it is a version of Health Anxiety. So I would say yes, you read constantly about a disease and the next thing you know, if your susceptible, you start to believe you may have the disease.
I hope this helps you some.
Moderator Anxiety ~ Panic Disorders
*~* Not a mental health professional at all *~*
Dx: Anxiety/Panic, Depression, GERD, Osteoarthritis
*Wife of a Crohnie*