Hello, I am a 41 years old man. During the Christmas vacation, I became tired and I started having tachycardia at 100 bpm and became suddenly unable to do any heart effort. For example, when I was walking outdoor, my heart rate was 140 bpm with strong palpitations. The tachycardia got worse by the end of february (120 bpm). Since the end of March, I now have about 145 to 160 bpm tachycardia when I'm standing and not moving and I am out of breath. I just saw my doctor and she scheduled a 24 hours holter. What do you think I may have? Should I worry? Because of this health problem, I have been unable to get back to work since Christmas now. Thank you!