Fetal Arrhythmia Possible at 20 week apt..Anyone else??

Went for my 20 week anatomy scan and baby is measuring perfect! Original heartbeat was 148 at beginning of scan and then while she was looking at the spine she saw it go down to 78. Noted for the doctor and she is referring me to a specialist to get a better look. Says nothing to worry about much because it most of the time corrects itself but it’s hard not to worry! Should go for my next apt next week, hopefully. Anyone else had this or any information? This is my third pregnancy but first time with this.