We had a great date, kissed, she told me to call..now she isn't responding!?

I went speed dating for professionals in the city and met this wonderful girl there (we are in our mid 20s). When I got the results and we had matched I emailed her and we ended up having dinner at an Italian restaurant. I think the date went very well and that we had very enjoyable conversation. We were talking and laughing for 3 hours and were the last to leave the place! Even two random older women sitting next to us at the beginning started complimenting me saying I looked like Dean Martin or something and that we were such a beautiful couple and what not which was nice. After the date we walked to a street intersection were our paths home forked and I kissed her and she kissed me back..I was a little nervous so it was a short kiss but then I asked her when I could see her again and she said maybe Sunday or Monday and to give her a call. This was yesterday and later that night I txted her just saying I had an awesome time..weirdly she didn't reply. Today at the gym I sent her a quick email with a funny reference to the Stanley Cup from dinner that had come out in the news and she also hasn't replied which is unusual because our initial email communication she would reply to pretty fast. What could have happened? I don't understand and I'm starting to have that awful knot in my throat feeling!! What is happening?