My main way of practicing metta has been to bring attention to the heart centre and let it rest there until a warm feeling arises. This warm feeling is metta in its barest form. During a two-week retreat in 2017 I decided to practice just that and see how much time I could spend in that state. By the end of the retreat it was all day long, and I would fall asleep glowing with metta. I would wake up halfway through the night and it was still going, which is a proof-of-concept that it can be sustained even while asleep. By the time I woke up in the morning it had faded away, but a few seconds of focusing the attention on the heart centre acted as a bellows blowing oxygen on embers and metta would burst aflame again to last the whole day.
As I mentioned before, the unitary experience tends to generate joy, which can be interpreted as a form of love, as one goes about one’s day. But sometimes there is a foreground-background reversal and it feels like awareness and love are filling the world, that the world is bathed in love. Now, because something feels that way, it does not mean it actually is that way. But I can see how practitioners with unscientific views of the world could come to believe, and teach, that consciousness and compassion are primordial elements. It is not necessary at all to adopt such a belief to experience life that way, and it sure is a delightful view to access. It is an impersonal form of love, there is no source, and everything is a recipient of it. It just feels like it is everywhere.