Eight months and head banging

I forgot to say, Erbie is 8 months already, and rolling like crazy. We've put a duvet down for him to play on but he keeps banging his head on the floor in an alarming manner. The GR and I were both knelt down today deliberately banging our heads until it made a similar noise. The GR was very concerned that he might be doing himself some damage. I found it quite difficult to actually let my head go so that it would bang. The GR was relieved when he did it, that it didn't hurt too much - just made a loud noise. I on the other hand when I eventually did release my neck muscle actually felt a bit dizzy, and have since been watching Erbie like a hawk and averting many bumps, by the end of the day thankfully he'd almost learnt to stop his head just before impact.