Answer:
During the vanavas, Pandavas were wandering in forests and once they felt thirsty. Then Yudhishthira has asked to Nakula to look for the water. He found a lake and when he is going to drink water, a hidden voice has warned him that he could not drink water before answering his questions. But Nakula has ignored that voice and drank the water and felt dead on ground. Same thing happened with Sahadeva , Arjuna and Bhimasen