Difference between systollic and dystoll

I am suffering with atrial fibrillation and grave hyperthyroid  for 16 months. Is there any risk if the difference between systollic and dystollic is reduced or increased. I feel normal when difference lies between 35 to 40. Like 105/68 which is my normal reading. But my bp n pulse increases  somedays during sleeping. Today I woke up during sleeping and was feeling uncomfortable when my bp reading was 117/62 (difference of 55) and pulse was 90. Some times my difference is 25. I feel confortable when difference is between 35 to 40. Second question is regarding a smart watch compatible with android phone. How reliable are smart watches for measuring ecg and monitor bp n pulse while sleeping. My bp and pulse mostly increases while sleeping. If smart watch is reliable, can someone suggest which smart watch i can purchase for my android smart phone (realme gt neo2).