If WordPress widgets suddenly jumped to the bottom of your blog, instead on the right as you expected, it’s most probably due to misformatted HTML tags in one of your posts. It happened to me and it took me some time to figure out but basically you need to find the offending post first. It’s a little time consuming but click on the individual posts from most recent to least. If the post is OK, you’ll see your widgets on the right. If it’s the offending post, you’ll see the widgets at the bottom. Once you find that post, take a closer look to HTML open/close tags. There’s most probably a missing close tag or something similar. In order to not run into this problem again, have WordPress check and correct your HTML syntax automatically as explained here.