PredniSONE and bedtime

Was prescribed prednisone 10mg dose pack. Took my first days worth and by bedtime my heart was beating so fast it felt as if it was going to pop out of my chest and burst. I went to the hospital and per the doctors there, SVT is not a reaction to prednisone. Anyways, left hospital with a clear bill of health, heart was in good condition.
Now, If it wasn't the prednisone that caused this rapid heart beat, what was it? I really think that the prednisone was the cause but as long as I'm not sure, I fear this will happen again out of the blue.

The moon face and weight gain did not occur until week 4. But I started really drinking a lot of water - at least 100-120oz daily. This helped the moon face considerably, as well as start me on losing some of the extra weight. Be careful of sodium in the diet - that is the reason for the bloating. So - tons of water (try to get it in early in the day, that way you are not rushing to fit in all that water close to bedtime) and working out four times a week helps with the moon face and bloating. But I still can't get rid of obsessive thoughts - such as cleaning my house or finding a good price on lemons. I hope that goes away when I am off the Pred.