According to the top-voted answer of this question:
When we sleep in this position, iron from the whole body starts to congregate in our brain which can cause headache, Alzheimer’s Disease, Cognitive Decline, Parkinson disease and brain degeneration.
Wow, it seems a bit surreal, especially when this other question say that it doesn't have any risk.
Did research after 2011 arose new problem? Or is it that Hindu guy horribly wrong?