I had answered a question rightly, I dont know why was my answer downvoted 4 times and I got -8 rep, and the question has also been removed.
You are probably referring to this Q&A which has now been removed:
To understand the 8 point issue - you had been upvoted once on your answer hence gained 10 rep points.
You have also been downvoted once - thus lost 2 rep points giving a sum of 8 rep points gained.
Community - the StackExchange robo-cleaner - has decided to delete the question:
- The combination of the question itself having answers with negative votes, no accepted answer, the question being closed and a question which has been negatively voted at some point.
These factors are amongst its main criteria to delete stuff.
Community does this to keep the site clean - the question, nor answers are no longer deemed worthy to keep around.
Thus when a question is deleted - through Community, owner activity, site-user activity - any rep gained within the last 3 months is automatically removed as well.