Many thanks for the very helpful post. I only found the following two passages in "Ten Recollections":
"Recollection of Stilling
This is peace, this is exquisite — the stilling of all fabrications, the relinquishment of all acquisitions, the ending of craving, dispassion, cessation, Unbinding.' — MN 64 [I recollect this paragraph often during meditation]
Among whatever qualities (dhammas) there may be, fabricated or unfabricated, the quality of dispassion — the subduing of intoxication, the elimination of thirst, the uprooting of attachment, the breaking of the round, the destruction of craving, dispassion, cessation, the realization of Unbinding — is considered supreme. Those who have confidence in the quality of dispassion have confidence in what is supreme; and for those with confidence in the supreme, supreme is the result. — Iti 90" [This paragraph is too long to recollect during meditation]
The reason I'm not recollecting the various virtues of nibbana but rather the peaceful state of mind I experienced before: after breath disappears, I need to focus on a single simple meditation object to enter samadhi, instead of scattering my awareness in the multiple qualities of nibbana. I tried to focus on the whole body [mindful of "there is a body"] or imagine the whole body breathes in/out, but distractive thoughts could occur. Recollection of the peaceful state of mind could better maintain the stillness of the mind in this situation. Since my focus now is samadhi, not vipassana, I suppose as long as a method can better induce samadhi, it might be fine (?). After my concentration is deepened, I can turn around to use vipassana to analyze its drawbacks.
Hello Goofaholix: thanks for your comment as well.