Only several times in my young life have I felt the "tunnel" as you call it. Except the nickname I give it is different. I call it the "other dimension" "Beast mode" "demon jacked" whatever you want. It gets corny but the "ultra zone" is real. Often I can feel my heart bump inside my chest and my breathing is often out of control. But the feeling is powerful and you don't want to stop. Which is what you experienced as you pushed yourself to the hardest you could.
You can practice hitting this zone with control and when you want. Just be careful!! You'll send your body into overdrive and can actually make yourself weaker by overworking yourself. As in it doesn't matter how much rest, food and stretching you do. If you muscles are having a hard time recovering after 3 1/2 days. Most likely you've hurt yourself more then you've helped. This is called over working.