What Causes Irregular Heart Beats After Strenuous Exercise?

Question: Hi I've experienced some strange things with my heart for the last two years on and off. I have never experienced nor does anyone in my family have problems with their hearth, but since I started weight training almost two years ago I started noticing something. When I do certain types of physical very demanding tasks I get very exhausted. Then some times around an hour after I finished my workout I notice my heart starting to do fast beats, like instead of normal beats they go like this: normal, 2-3 fast beats, normal and so on. Sometimes it feels like it skips the normal beat. After 1-3 hours this goes away as fast as it appeared and I don't notice anything with my heart until after very demanding weight lifting exercises usually the ones for my cores and stomach area. I notice I struggle with proper breathing techniques while lifting, and I don't feel anything with my heart normally. I notice a kind of anxiety when my heart beats faster. Since I didn't use to excersice since I was a young teenager, then getting a high pulse somewhat scares me. I'm also not so big, only weighting 63 kg. My heartbeat at rest is around 55-65 and blood pressure is normal. I have been out of shape for many years and this kind of makes me scared of continuing with the exercising.

Thank you for your answer, I will follow up with my own doctor but I have to wait some time. I was wondering if this could be caused by anxiety or a similar effect, since I started exercising I fear it happens and I wonder if the fear causes it to start? I usually don't get it from doing cardio, and it starts hours after I'm done training and not while training. Should I stop excersicing until I get this checked or is there anything else I can do? Also could it be caused by not having done any excersicing and being in bad shape?