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Just hit "ctrl R" or refresh the page, or click back and re-click where you wanted to go.
If posting, then it is possible it did post, sometimes it does, sometimes not. Do not click "send again" which post again. Click back to previous page, copy your post so you have it and click refresh to see if your post is there. If not then you can just paste it again, not retype it, since u just copied it.
This is not a big deal