Impossible to be 100% sure. But he wasn't seen anywhere on April 15th, a very important date for North Korea since it's the birthday of Kim-Ill Sung, grand father of Kim-Jong Sun and founder of the regime.
Daily NK, a news website created by North Koreans who fled the country to the UK, recently reported that Kim went through heart surgery on April 12th
Other sources reported other news but most of them are incoherent one towards another.
The only thing that can be stated is that he hasn't been seen since April 11th. In 2014 he disapeared for 6 weeks before reappearing, using a walking stick.
His predecessor, Kim-Jong Ill had died days before it was officialy announced and his death had took everyone by suprise.