Heart rate at rest 120, on steroids due to asthma - overweight vicious circle of breathlessness = lack of exercise - how worried should i be?

Concerned: Depending on your physiologic stressors (asthma, poor conditioning, other?), a fast heart may or may not be physiologically appropriate but chronic heart rtes in this range are not healthy. An ECG and perhaps ambulatory monitoring might assess for the possibility of arrhythmia. A good pulmonary program might help more with the asthma. Once feeling a little better exercise, weight loss

Cyclic trap: Yes. The oral steroid/asthma/under-activity/obesity cycle is easy to fall into and difficult to escape. However the tachycardia is not necessarily associated and may be a marker for other organ system(s)(cardiovascular) involvement. You need to see an asthma specialist and if you have, see another one. Otherwise this will only get worse!

BETA AGONISTS?: If you use proventil, albuterol, or alike quite often you can have tachycardia because of that.