Hmm, at 4 months babies do a lot of head turning, it's normal exploration, lah! But kalau dia pusing 3-4 kali berturut-turut sampai macam repetitive gitu, or kalau followed by other movements yang tak biasa, better check dengan paediatrician just to be safe. A few of my mum friends pernah paranoid juga, turned out fine, but you know lah, peace of mind worth it! Is he otherwise happy and hitting his milestones okay?