As said by Lord krishna in bhagavatgita :we create our own karmas and its consquences comes to us whether good or bad.First what is karma means action and it means good or bad anything.So we all as spirit souls lived in the past in various bodies and living and taking up various bodies according to the karma that we have created and keep on going.But we are eternal beings trapped and living a conditoned souls compelled to take up a body according to Lord krishna instruction to nature prakirti and we get birth,death,diseases and old age.So humans suffer a lot when first diseases hit us and one way its a blessing (now this might sound weird) but they are for our good and cleansing our souls and it is the order of the lord for us to realise and question who am i? and there will be a point of self realisation that as we are not here for pleasure but to be a simple tool of the lord and love lord unconditionally without anything in return.so in that stage all your bad and good karmas also end and come to a neutral state where sarva karna karanam is lord krishna.Also it requires blessing of the Lord to come to this point and so we start developing prema or bhakthi towards the Lord and accept his path towards reaching him back to join in the spiritual world. Now as going karma and diseases where human birth is very precious we need to get out of this entanglement and surrender to the Lord but instead we get caught by Maya which is also created by the Lord since we are not ready and evolved into a full mature soul since desires are still ruling our mind. And because of desire greed is developed and so anger and so it turns into a very big bag of bad karma.As lord krishna says kama,krodha,loma as the gates to hell.Its true for example:If a person eats Fish in a birth to satisfy his toungue pleasure and dies finishing that birth and in the next birth he or she is born with asmatic complaints and breathing troubles as we made to suffer the jiva and enjoyed its flesh.Though the soul doesnt have any pain still the soul has got a body to enjoy the material world from the Lord. Now another example for this is like in a lecture i heard that where a listener questioned the speaker :if a child is born blind so the parents also suffer so the karma is with the child or the parent.The speaker replied the child in the previous birth would have hurted some jiva in the eyes and two other people would have supported the act of cruelty.So now the karma bond is created between these three and so the person who hurted is born as child for the two people are parents and so repay back the karma and realise and evolve. Another example Who insults others, breaks promises, causes great disappointment to another, deprives one of his property, disgraces others in public will get the birth gets mental agony and pain. This is true because in my life experience itself i had.I was born and my mother passed when i was six and father never turned up my grandmother (mother side) took care of me but she would insult from that small age and was physically and emotionally abused till the age of 24years for which i was under depression for 6years and attempeted suicide because of the agony and on top of it i have developed a very rare disorder called premature ovarian failure where it is 1% in 100000 women occur where menopause has occured at the age 15 where practically i have menstruated normally only thrice till now 17years.So its my karma i have created and repaying but i am recovering after i started to surrender to the almighty and many miracles have occured. So how to overcome this is by surrending to the lord and nama japa hare krishna hare krishna krishna krishna hare hare:hare rama hare rama rama rama hare hare is the only way to get out of sins.Read the scriptures given by acharya srila prabhupada in iskon Bhagavatgita and srimad bhagavatham and the eyes will be opened.