Sudden Energy Boost from Hot CoCo

I am 45 years male who recently bought an elliptical trainer. I have
been exercising for a month on the machine and I am up to 30 minutes
workout time. At 20 minutes I usually begin to get tired and it becomes
difficult to keep the heart rate up.

Few days ago 1 hour before exercise I drank a cup of hot chocolates.
When I started to exercise two things happed.

1. I had to keep my heart rate down instead of working hard to keep it
up.
2. The 30 minutes felt like a 10 minutes workout. I could have easily
gone another 30 minutes.

So I am thinking is it a good idea to have caffeine or other metabolic
boosters to help with my work out? Whatever was in hot Chocolate
Caffeine or sugar made the exercise so easy this time around. I do not
drink coffee and hot chocolate only occasionally in winter.