My heart just went Beatbeat-beatbeat-beBOOM (thud)-1secPAUSE-Normal beating starts again. Normal? PVC / ectopic? ECHO, X-ray, blood test 100% normal.

PVC. Very likely a PVC as the are extremely common, but could be some other less friendly problem with cardiac rhythm. If is persists you may want to consider a Holter Monitor or an event recorder.
Palpitation with 1 s. Palpitation with 1 sec pause may be early sign of sick sinus syndrome.It may also occur as cardiac arrhythmia(svt,vlc,mutifocal atrial tachycardia),mitral valve prolapse,coronary artery disease,hypertension,cardiomyopathy. Diagnose by 24 hour or long term holter monitoring,EKG,echocardiogram,stress echo,EPS evaluation,lipid profile. treat the cause,beta blockers,pace maker evaluation,cardiac cathe.