Sunday is a very sacred day in Indian spirituality. It is today called Maha Shiva Ratri - The Great Night of Shiva. On this day spiritual seekers stay up all night, paying homage to Lord Shiva the Hindu deity related to destroying the weaknesses that hold us back from being our all-powerful True Self.
It is customary to fast all day -- stay up all night and (perhaps) offer Bilva leaves to a Shiva Lingam (representation of the God) throughout the night. In modern times it is customary to say the thousand names of Lord Shiva and/or other sacred mantras such as the "Maha Mrityunjayaaya Mantra" (the great victory over death mantra) and sing songs throughout the night.
Lord Shiva is the most sought after of the deities and in many ways the hardest to abide with as his lessons are the very lessons of life (and death) itself. Who we are beyond just the physical body is the abode of Shiva. Our ego trembles at the feet of Lord Shiva because his presence means the death of the ego - the death of the smaller self. The true Self and the smaller self cannot exist simultaneous - just as darkness cannot exist in the presence of light. It is said that Lord Shiva is the easiest to please, he accepts all who are sincere in their desire to transform.

AUM NAMAH SHIVAYA