Hamas has refused to import Israeli diesel because of taxes imposed by the Palestinian Authority.

Having gotten used to years of scheduled blackouts, generally eight hours without electricity two of every three days, Gaza’s 1.7 million residents are now facing daily power failures of 12 or even 18 hours.

Businesses have cut back production, hospitals are rationing electricity to keep dialysis and cardiac support systems running, students are doing Internet research in the middle of the night and battery sales are brisk. Everywhere, the drone of generators mixes with the odor of kerosene lamps.

Nema Hamad, who is 64 and has sleep apnea, struggles to keep from suffocating. Some nights, her sons run improvised lines from neighbors who have electricity to keep Ms. Hamad’s airway pressure mask working. Three times, they paid $100 for Ms. Hamad to sleep in a private hospital. Once, she woke up gasping for air when the electricity went off unexpectedly and ran into the street, desperately looking for oxygen.

“This is not a life,” Ms. Hamad said as she sat on a mattress in dim candlelight. “Sometimes, I fear that it might be the last time I sleep.”

The electricity shortage comes a year after eight days of intense cross-border violence that killed 167 Palestinians and six Israelis, and it is a profound sign of how Gaza’s situation has shifted since then. The past 12 months have been the quietest in a decade in terms of fire exchanged with Israel, though Israel’s air force struck a weapons facility and two tunnels on Tuesday night after reports of rocket fire near Gaza’s border earlier in the day. Israel has also eased some of its restrictions on the strip, but political changes in Egypt have left a siege of another sort.