First, I had to look up that word and make sure I knew what it meant! Looking back on my life, I would pinpoint two time periods as my halcyon days. The first period was the summers when I was about 8-10 years old. I can remember playing in the creek that ran by our house, floating boats that were just scraps of wood from Daddy's projects, and chasing crawdads under the rocks. I picked big, juicy blackberries up on the hill behind our house. I invented a 2-room playhouse in a section of of smaller trees on a slope east of the garden, and played with my dolls there. As the youngest, I had fewer chores than the older siblings, and more free time.
The second period of halcyon days was when all of my children had moved out and my husband was still working. I only got to enjoy 11 months of empty nest, but I loved it. I could wander from one little task to another all day, eventually getting back to where I started. Nobody asked me questions, nobody got in my way, I could think out loud all I wanted to, listen to whatever music I wanted to, eat when I felt like it, and let my mind relax.
Then the kids started moving back home, and then my husband went on a medical leave of absence followed by retirement, and those days will never come again. I didn't know it would only last less than a year, rather than the expected five years.