On normal occasions, the feels occur with fictional phenomena such as character deaths, sad moments, happy moments, and generally extreme emotions towards someone/something fictional. The term "UGH THE FEELS" Is probably only going be used by fangirls/fanboys.

The intense emotion of a fandom.

The Feels is in the same family as the Succubus/Incubus. However, it feeds not on lust but on the soul energy released when a human heart bursts. To that end, the Feels will come to those witnessing or living through a particularly moving moment when their heart is fullest and add additional emotion until the heart can no longer contain the pressure. Despite the pain and panic this causes, many victims of The Feels will intentionally seek out material that makes them vulnerable to it. Scientists argue whether this is the result of brain damage in those individuals or if The Feels delivers an addictive surge of dopamine to ensure future feedings.

Studies have been hindered by extreme limb flailing and the incorporeal nature of the soul.
Researched by "Siwenna" of the interweb

Shortened version of 'feeling', generally a strong emotional response.

to understand; relate

Something you will never fully understand.

The way one reacts to an event; the sensation caused by touch; A sensation not felt by chuck norris or Ray Charles.