Did Our Best Moment last —

Did Our Best Moment last —
'Twould supersede the Heaven —
A few — and they by Risk — procure —
So this Sort — are not given —

Except as stimulants — in
Cases of Despair —
Or Stupor — The Reserve —
These Heavenly moments are —

A Grant of the Divine —
That Certain as it Comes —
Withdraws — and leaves the dazzled Soul
In her unfurnished Rooms –
                                 F560 (1863)  J393

This poem shares some of the bitterness of one of her early poems about the painful transience of the divine encounter. There, Dickinson complains that "For each extatic instant / We must an anguish pay" [F109]. Here, the cessation of divinely-granted "Heavenly moments" induces something like opiate or cocaine withdrawal. Coming down from her great high, the "dazzled Soul" finds herself back in her "unfurnished Rooms". 
Dickinson makes the parallel to drug use quite explicit. There is a risk to partaking in divine bliss; only "A few" manage to obtain it. God, or "the Divine", well aware of the danger, doles these moments out. They are only given "as stimulants" when the seeking party is suffering from "Despair" or "Stupor". The Divine grants these moments and always withdraws them. The danger of addiction is mentioned in the first two lines. If these heavenly moments weren't cut short they would come to seem better than heaven itself. Real earthly life isn't a bit like heaven, so such addictive thinking must be kept in reserve.

We can chart these swings from peak to valley in Dickinson's poems. There are poems of Despair, those of stupor or numb paralysis. But there are numerous poems where Dickinson describes bliss, ecstasy, transport, and rapture. Would modern students see evidence of bipolar disorder? Perhaps, but regardless of what engendered these episodes, Dickinson explored them as terra igconita and used them as touchstones for poetic truth. 
Who else could conjure the coming down from a divine high as a "dazzled Soul" finding herself alone in "unfurnished Rooms" as if she had been soaring in high places only to wake up in a drab and deficient habitation of flesh and blood. Such paucity of the flesh is implied, such parsimony of the divine – and such irony in how much emotional force is delivered in a poem that until the last lines reads as an extract from a Catholic or social studies text. 

Sherlock Holmes – who enjoyed cocaine

Dickinson would have some familiarity with the effects of narcotics. During her lifetime, the British Empire was vigorously promoting opium use in China. Cocaine and opiates were famously used by such prominent writers as Thomas De Quincy (1785-1859) and Samuel Taylor Coleridge (1772-1834). Poets Lord Byron, John Keats, and Percy Shelley were known to take laudanum on occasion; and Gabriel Rossetti's wife Elizabeth died of a laudanum overdose a year before Dickinson wrote this poem. Sherlock Holmes, perhaps the most famous fictional cocaine addict, was also a Victorian creation. Scottish writer and doctor Sir Arthur Conan Doyle first started writing about him in the 1880s.  
But while these figures may have hoped drugs would help deepen their perceptions and provide an altered state, Dickinson tastes "a liquor never brewed" and is an "Inebriate of air … / [a] Debauchee of Dew" [F207]. Indeed, she finds something "Transcending ecstasy" in a simple "summer's noon" [F104].