Heart racing everytime I have a half can of cider/beer

So well I’m supposed to stay away from alcohol due to the fact that I ended up being addicted to it however I act on the urge to have 1 drink every now and then. When I do my heart races really fast and it gets uncomfortable and it never used to be like this when I was drinking everyday for 2 and half years and mixing my alcohol with other substances. Now I’ve been sober for 10 months with the odd slip up of having a half a can of cider or beer but never get inebriated because of this awful side effect that I now deal with. Anyone know why this has happened? Today I’m struggling with the urge and cravings to get drunk because I feel down and anxious but I don’t want to have my heart racing.