Lately, after napping during daytime, I get a bad taste in my mouth when waking up. What could cause it? (sympts gas, bloating.)

Bad taste. Sounds like you might be having some esophageal reflux of stomach contents into your esophagus causing the bad taste. You might want to try sleeping/napping with your head elevated slightly - or seeing if using an over the counter antiacid or medication like otc Prilosec might change it. Silent aspiration can become concerning - you might want to mention it to your doctor.
Possibly reflux. Are you napping siting in a chair or laying down? If laying down, then it may be more likely that this could be symptoms of reflux. Stomach acid can come back up into your esophagus and even give you a taste. There are some over the counter antacids or acid-reducers for which you may be eligible. Please speak to your doctor about which may be right for you.