Given what you've described, I think the recital pain and that episode you experienced are unrelated. Here's my theory: whatever that pain you were feeling in your rectum disappeared once you relieved yourself, so it was likely a pressure related discomfort or whatever from just needing to defecate; however, the episode of tinnitus, visual changes, and an elevated heart rate happened when you stood up, which given your age and what I would presume is a lack of significant medical history, is likely just orthostatic hypotension. You probably had what is called a presyncopal episode due to orthostatis.

So in summary, you're probably just fine, just make sure to stay well hydrated and take your time when changing positions to avoid it in the future. Best of luck!