It struck me — every Day —
The Lightning was as new
As if the Cloud that instant slit
And let the Fire through —
It burned Me — in the Night —
It Blistered to My Dream —
It sickened fresh upon my sight —
With every Morn that came —
I thought that Storm — was brief —
The Maddest — quickest by —
But Nature lost the Date of This —
And left it in the Sky —
Fr636 (1863) J362
We are eased into this intense poem by Dickinson's ambiguous opening lines. "It struck me" is a common way of introducing an insight or new idea. A particularly brilliant insight might come as if by a stroke of lightening. And so we might begin reading the poem in expectation of one of Dickinson's knifing epiphanies or surprising twists on ordinary wisdom. But we soon realize the strokes of lightening as bolts of sheer pain.

Her technique here impresses me. Through the first stanza I'm excited by the lightening and its Fire. The dash ending the stanza carries suspense across the stanza gap and into 'It burned Me'. Whatever the lightening might mean, it suddenly seems painfully piercing. We experience a bolt of understanding just as the first line promised and just as the stanza descends into horror. Fire blisters to the speaker's dreams as if they were tangible entities scorched and disfigured. This happens every night. And every Morn her sight is 'sickened', withered, I imagine, as a lightening-struck tree.
The poem ends with no closure. I think it might be read, "I thought that Storm would be brief" and the worst part would be over soonest. Experience and convention lead us to that belief: pain must ebb: the intolerable fade to the tolerable, whether in sickness, love, or war. But Nature is not natural here. Nature 'lost' track of the situation, left it looming in the sky.
Dickinson leaves no doubt about the source of her pain. It comes from above, it is fire waiting for a slit in the clouds, it is lightening day and night. The realm of sky – heaven – is not one she can control. The gods forge the lightening and Jove hurls it. The Christian god punishes and blinds, perhaps to force a truth, as with Saul of Tarsus (New Testament, Acts 9: 3-16).
In a somewhat similar poem, '"Twas like a Maelstrom, with a notch',
Fr425, written a little over a year earlier, the intense 'Agony' ends 'When God – remembered'. In the current poem God is not there and Nature has forgotten.
In other commentaries, this poem is considered to be about Dickinson's eye problems. In the same year as this poem, 1863, Dickinson wrote to Thomas Higginson that 'I had a terror since September – I could tell to none' (L261). In 1864, Dickinson stayed in Boston for eight months of therapy with a prominent ophtalmologist. Reflecting on the experience in an 1865 letter to Joseph Lyman (friend of the family and a near-suitor for sister Lavinia) she wrote:
Some years ago I had a woe, the only one that ever made me tremble. It was a shutting out of all the dearest ones of time, the strongest friends of the soul – BOOKS. The medical man said 'avaunt ye tormentors.' He also said, 'down, thought, & plunge into her soul.' He mmight as well have said, 'Eyes be blind, heart be still.' So I had eight months of Siberia.
But while the poem might draw upon the pain and dread Dickinson's eye afflictions caused her, I think she intends it more generally. There are piercing pains that never go away. There are also times, glimpsed in other Dickinson poems, when like for Saul, Divine knowledge assaults and flays, as in 'He Fumbles at your Soul
(Fr477) when God's 'Imperial Thunderbolt' / … scalps your naked soul'.
Sometimes I feel that Dickinson hurls poems like bolts across the ages.