Alamak, tu normal je lah, baby startle reflex dia! Mine did the same thing at 3 months, kejut sendiri kalau dia overtired or when transitioning between sleep stages, memang biasa la. Tapi kalau dia terkejut sangat frequent sampai affecting his sleep or dia nampak uncomfortable, boleh la mention to your doctor just to be safe, tapi honestly most of the time ni just part of being a newborn je. A few of my mum friends also had the same thing, and their babies outgrow it by around 4-5 months.