This happened to me, in a dream. I was in a relationship with her, I was back in high school in the cafeteria. I was sitting down on a long table, and she was there. She was sitting next to me, and I laid my head on her lap. She stroked my head, and I was surrounded by light and warmth. She comforted me, and for the instant before I woke, I was truly happy.
I've had only this feeling once before, when I woke from my surgery, buzzed on an IV drip. I felt harmonious, at peace. Her hand in my hair, her truly loving me, caring for me, it was so powerful. I woke to find a sunbeam hitting the side of my face I was resting on her lap on.
I've also never been more terrified, because in both cases, the dream and the surgery, I went through a small period of time afterwords where I desperately wanted those feelings back. I was going through a mini withdrawal, and feeling powerless to these feel good things is a clear sign to me I would fall to drugs hard and never get out, and become dangerously attached to any committed relationship with anyone. I'm too emotional and too dependent, and any break up would devastate me.
