I want to know that What kind of past deeds led Bhishma Pitamah to suffer on Bed of Arrows in Mahabharat battle. Is there any karma theory relate Bhishma Pitamah to be in the bed of arrows? or any incident ?
Bhismah Pitamah had a boon of Ichha-Mrityu , So unless he didn't want, nobody could have killed him. He wanted to die proudly as Kshatriya. So he requested Arjuna to make bed of arrows.
For Karma-Theory that why he had to undergo of loads of pain and struggle of human life, Read this post: https://hinduism.stackexchange.com/a/27333/647
It has the story in detail.