The "element of blank" (line 1) describes how pain clears or empties life of other experience. We are aware only of pain, as the word "infinite" (line 6) suggests.
"Enlightened" (line 7) is ironic. Enlightenment is insight which enlarges our intellectual or spiritual understanding or enhances our knowledge. The enlightenment which pain brings is the realization that the future holds more and still more pain. Is this an enlightenment we would gladly do without?
"New periods of pain" (line 8) seems to contradict the idea of unbroken continuity in lines 1-7, but this is probably not meant literally, unless we assume one "period" to be followed immediately by another "period." Or does this phrase mean that pain succeeds pain, without stopping, just as one period of time succeeds another without interruption. How do you read this line?