According to locals, the low-voltage that courses through one's body when lying on train tracks can trigger a healing process.
The Jakarta Post interviewed a woman about this strange practise:
[A woman named] Kusmiati, who said she suffered from asthma, high blood pressure and diabetes, is one of many locals who routinely undergo a unique alternative "therapy" in which one lies splayed out on the railway tracks near Rawa Buaya train station in Cengkareng, West Jakarta.
The "therapy" involves placing one's hands and feet on the steel rail tracks. By touching both sides of the tracks at once in this manner, one receives a low-voltage electric shock, which locals believe is a potent cure for many diseases.
The locals said the method became popular around a year ago when a taxi driver allegedly recovered after suffering a stroke, by frequently lying on the tracks.
Today, the therapy is attracting more and more people, from locals to people who travel from far away to experience the reportedly soothing effects of the therapy [...] Their growing fondness for the treatment soon saw them adopt the "therapy" into their daily routines. Every afternoon from around 4 p.m. to 5 p.m. there are typically 10-15 people lying on the tracks.
First off, don't try this. There is no evidence that low-voltage will help cure any condition you have and there is a real danger of being killed by an oncoming train.
Secondly, this is a fairly new 'fad' but it's also the beginning of a new piece of folklore. I hope that people stop doing it because, well, it's ridiculously stupid, but it's also an interesting look at how a folk remedy could have its origin.