If you accidentally swiped away all notifications, there's a way to look at your notification history on Android. You do need to turn it on first, though.

世界的に重大なこの問題に、解決策が登場しました（Androidのみですが）。 『Notification History Log』はスマホに表示される通知を、1カ所にまとめて保存してくれるアプリです。

You can see old notifications on an Android that you've previously cleared via the device's Notification Log, which is accessible in Developer Mode.