Spike Protection Activated -- why?

I just got the email saying Spike Protection has been activated. How can I tell what’s causing it? I do have one error that constantly spews from one IP address once a minute, but I have that filtered out so it shouldn’t be counting against anything. Is there any “see all recent events” view in Sentry? I just have the Developer plan. In my Stats view I just see the 60 filtered events per hour and nothing else, and nothing has changed (as far as I can see) in the last 24 hours.