Are you given sick or abnormal statuses when fighting enemies? If you cut your sleep time too long, you may not recover even if you rest for 8 hours. Try sleeping until morning for a few days in a row, or if you're sick, try taking medicine.
Thanks I'll try sleeping a few more times!
np(: If there is a part displayed in red letters on your status screen, it is a bad status, so please check it as well.