Hello, madame. Thank you for your question and welcome to HCM. I understand your concern. During sleep, there is a phase which is called rapid eye movement (REM) phase, being one of the five phases of sleep (the other four constitute the non-REM phase of sleep), during which there is the highest activity during sleep and a flush of catecholamines (e.g. adrenalin and noradrenalin) to the system is a characteristic. Their effect on heart rate is well known, which act by raising it. If this is the case, then I assure you there is nothing to worry about. However, since you are a 57-year old lady, I would also recommend you to run some tests: - complete blood count (CBC) and - thyroid function tests (TSH, fT4, fT3). Feel free to ask again. I hope I was helpful. Take care.