More about the term Neurosis

Sigmund Freud redefined and popularized Neurosis diagnosis in the 20th Century

Could not be explained physiologically - and this is the key - it is kind of a strange anomaly of the medical field where people are complaining about physical symptoms, but there's no underlying cause, apparently. There's no underlying physiological cause like an actual lesion or cuts or a tumor or anything like that...

Neurosis people will immediately think of Freud's landmark paper on the case study of the Ratman. People think of obsessional neurosis.

Freud believed that when  a person is unable to consciously process trauma from the past. 

They repressed the agonizing feelings related to the event. And this is a really important function that we need to know is that - the mechanism of is repression - Is the suppression of what is deemed to be unacceptable or traumatic or uncomfortable or whatever it may be producing an undesirable unpleasant feeling. That then gets repressed and over time. The individual does not recall the original incident at all. Instead, they exhibit a series of nervous symptoms such as anxiety, sadness, perfectionism, irritability, low self-worth, phobic avoidance, and obsessive thoughts. 

And this is what we mean by Neurosis.