Sleep has been one of my biggest challenges because mine has been poor due principally to anxiety, diagnosed mild sleep apnea and quite possibly other reasons. I appreciate good sleep is so important to many functions of the body not just the heart, so....
First I spent an hour in the evenings before bed practising Mindfulness, a couple of yoga exercises & prayer. This helped but I needed more so started using Breathright nasal strips at night. Still not good enough, so over the last month I have been doing slower breathing exercises (James Nestor's new book 'Breath') on my daily walks and I have taped my mouth closed at night (not practical if you have a cough or cold).....it's early days but without going into the science my sleep ( & energy) over the last 2 weeks has been excellent, the best for years!!
Re the mouth taping don't panic. Yes, I was a bit concerned on the first night, even though I had read about it; you soon forget about it and I wouldn't be without it now. It is not a big piece of duct tape, I use a small 2cm x1.5 cm piece over the top & bottom lip in the middle. I ordered myotape.com & cut them up so it works out at a very low daily cost. Also because it is so small it can still be applied if you have a beard.
Tips: Make sure your nose is nice & clear before retiring and if you like a sip of water during the night put a straw in your glass.
Caveat: This is only my personal experience of someone 67yo in otherwise good health with just Lone PAF and only on Flecainide, in case it helps someone else out there. Check with your medical team BEFORE any action if you have complex heart, respiratory or other health issues.