Uy, please message your OB agad or schedule a follow-up check, hindi normal na biglaang hindi marinig ang heartbeat, lalo na kung naririnig before, kaya importante talaga to check ASAP! One of my mum friends din nag-worry nito, at ang OB niya nag-explain na sometimes it's just positioning ng baby or ang dating ng doppler, pero kailangan talaga makita ng doctor para ma-rule out any concerns at ma-ease your mind. Wag mag-antay, mommy, better safe than sorry, especially at this stage! Thinking of you.