Heartbeat

I have a question about fetal heartbeat.  I went in for a ultrasound at 6 weeks and 2 days the heartbeat was 153 bpm, then I went in again due to some bleeding over the weekend at 6 weeks and 6 days the heartbeat was at 118 bpm.  Is this normal?  Why does it differ so much?  I know when I went in on Friday, I was nervous and stressed a bit due to the bleeding.  Then on Tuesday when I went in I was more calmer and relaxed.  Does that have anything to do with it, or is there something wrong with the baby?  Thanks in advance for any advice.  We don't go back to the doctors for another 2 weeks.  The ultrasound tech was not concerned with the differences.  She was the same one who did it on Friday.  

[cocacolapanda]

The baby's heart rate changes just as yours would.  If you are going for a nice walk or doing some other type of activity that brings up your heart rate you'll be higher, When your sleeping your heart rate goes down into resting mode.  So when the heartbeat was 153 the baby was active, at 118 the baby was most likely sleeping.

[growingbabyforyou]

Thank you for your response, it makes sense that way.  Yesterday I had another ultrasound I am 7 weeks and 6 days and everything measured perfect and the heartbeat was at 163 which they said 'is Great!'  We're thrilled!  It's also grown you actually can see some form of the baby already.