How did Ivar the Boneless die in real life?

Related questions

1. Is Ivar the Boneless real?
2. Does floki die in the cave?
3. Why did Vikings have beards?
4. Does floki kill Bjorn?
5. Are Bjorn and torvi married?
6. Does Rollo kill Ragnar?
7. Will Vikings have a Season 6?
8. Does floki kill Rollo?
9. Where does floki die?
10. Was Bjorn Ironside a real person?

Tags

1. #possibility
2. #mentioned
3. #sobriquet
4. #death
5. #unidentified
6. #sudden
7. #disease
8. #horrible
9. #raises
10. #struck
11. #source
12. #cause
13. #norse
14. #provenance
15. #other
16. #effects
17. #crippling