Test this by logging out and see if it loads quickly again. If so, then yeah, you're being artificially slowed down.
Edit: I actually just noticed it was slow for me too, logged out and it was still slow. No idea then.
Edit: Actually I just realized your theory never really made any sense. What site throttles bandwidth just to you when you get downvoted? Nutty theory actually.
After getting down-voted a certain amount you get hell-banned. Your posts are still posted, except only people with "show dead" enabled see them.
Before that however you just get throttled and the site loads more slowly.
(http://www.codinghorror.com/blog/2011/06/suspension-ban-or-h...)