Dear Ramesh Surya,
I recommend you write an application to the head of the organisation explaining the facts. The tone of the application should be formal and avoid informal words or phrases. Instead of "uninformed leave", write, "as I was sick, I could not obtain proper approval from my reporting manager and it was considered as "unauthorised absence".
Going further, you may write, "My unauthorised absence was considered as misconduct and my services were terminated. Termination of services is a punishment of the highest kind, however, if my candidature is ignored because of my misconduct in past employment, it will be double punishment. In view of this, my candidature may not be viewed against what has happened in the past."
Final comments: - The tone of your post is informal. You have written it casually as if you were informing some incident to your friend. The person with five employments behind him was expected to know how to write posts on a public forum. Well, gentleman, the sooner you get rid of this casualness, the better lest it will hold back your career's growth.
Thanks,
Dinesh Divekar