This is a very common arrhythmia. There is an undue awareness of the heart beat which is present much of the time, there are no clearly defined episodes. The heart rate is not that fast, not usually more than 110 beats per minute, though on exercise this can become very rapid (inappropriate sinus tachycardia).
There is not suually any underlying heart problem, though an overactive thyroid should be excluded with a simple blood test. An echocardiogram may be useful to exclude structural heart disease and if there is also breathlessness a lung scan may be needed to exclude problems there. A very rare tumour of the adrenal gland (phaeochromocytoma) may need excluding with 3 24 hour urine collections for catecholamine metabolites.
Again very common. this is a feeling, usually at rest, of a missed beat and a thump. It usually goes away if you get up and do something; it can be noticeable lying on the left side in bed.
It is almost never a serious problem though may need checking out with an echo. Symptom relief can be provided with a bet blocker or the rhythm controlling drug flecainide, which can be used as required if the arrhythmia is intermittent.