Speluncaphobia

Whilst many people would not regard caves or underground spaces as a cause of fear, it has been discovered that as more and more people from the surface world of Kelbonnar's Material Plane venture down into the depths of the Underdark for more and more extreme lengths of time, many become adversely affected by prolonged exposure to the subterranean region. 
For some, speluncaphobia can simply be an increased level of anxiety when in the more enclosed confines of the Underdark's caves and passageways, but for some it can develop into a crippling inability to do anything, as the oppressive nature of the place drives them slowly insane. 
Occurrences of speluncaphobia are often what makes denizens of the Underdark, who are naturally immune given that they are naturally subterranean creatures, believe that surface dwellers are weak willed and coddled. However, even the most stalwart trader, brave adventurer, agent of the Imperial Inquisition, trained to resist torture and deprivation have succumbed to speluncaphobia and never managed to return back to the surface world they so desperately crave to see again.

Causes

It is unknown exactly what triggers episodes of speluncaphobia. Some simply say that it is simply prolonged exposure to the more cramped conditions of the Underdark, but many travellers in the region who originate from the surface world never suffer from the condition at all.
Some have hypothesised that episodes of speluncaphobia correlate with exposure to deeply stressful situations encountered in the Underdark, encounters with the region's more alien denizens or wicked, feral creatures or even proximity for prolonged periods to Kinitiki gemstone. Those in support of this theory believe that encounters, or multiple encounters involving one of these three things may subconsciously drive the afflicted into a heightened state of stress, which convinces them that every aspect of the Underdark is striving to kill them.
It has even been suggested that lack of vitamin D from sunlight it to blame for the condition, and that the prolonged denial of sunlight imbalances the afflicted's mental state and causes the downward spiral into speluncaphobia.

Symptoms

Symptoms of speluncaphobia initially include:

• Anxiety
• Paranoia
• Feelings of dread
• Increased fear of confined or dark spaces
• Insomnia

In more serious cases symptoms include:

• Hallucinations
• Heart palpitations
• Schizophrenia 
• A crippling desire to get to the surface world

The latter symptom is by far the most serious, as it often exhibits itself as a mania that drives the patient to try and get to the surface as fast as possible, without regard for their own safety and often without regard for direction either. If sufferers of speluncaphobia who reach this last stage are allowed to do as they wish, they will often careen off in a random direction, convinced that it is going to lead them to the surface, after which they become quickly disorientated and become lost. Most who reach this final stage die, whether through exposure, malnutrition or being picked off by the creatures of the Underdark to whom they are easy prey.

Treatment

The most obvious way to treat a bout of speluncaphobia is to get the afflicted to the surface as quickly as possible, with exposure to sunlight being known as a surefire cure for the condition.  
Often this is not possible, so another relatively effective treatment is to get the patient into a well lit, comfortable space, where they can feel safe and rest until the episode passes.

Prognosis

Speluncaphobia has never been documented as being the direct cause of anyone's death, rather it leads people to make delusional decisions in its later stages that lead to death. 
Those afflicted by the condition generally recover if it is recognised and a requisite period of rest, ideally outside of the Underdark is administered. However, for some, a serious bout of speluncaphobia renders them incapable of ever descending beneath the ground again.

Affected Groups

The condition exclusively affects those born and raised on the surface of Kelbonnar's Material Plane, and it is known to especially affect:

• Dragonborns 
• Elves 
• Halflings
• Humans 
• Tieflings

Dwarves and Gnomes have been known to suffer with the condition, but it is much rarer amongst them.
Naturally, given that the condition is only really a problem for those travelling in the Underdark, demographically it tends to be traders, merchants, mercenaries and adventurers who have business deep below the surface that contract speluncaphobia on the whole.

Type

Mental

Origin

Natural

Cycle

Chronic, Acquired

Rarity

Uncommon

Affected Species

• Dragonborn
• Human
• Tiefling
• Halfling
• Elves