Alarms play at max volume

Most likely, your Backup alarm went off after your regular alarm failed tp wake you up. T Backup alarm is triggered when there is no interaction (no snooze, no dismiss) for more than 20 minutes.

Make sure you are using a loud enough volume in Settings → Alarms → Ringtone, or enable Gentle Volume increase in Settings → Alarms → Gentle volume increase

Try vibrations (Settings → Alarms → Vibrate).