Rome did in fact experience a deadly wound to one of its heads when Nero took his own life, after he took the lives of all his relatives leaving no successor in 68 AD. Rome entered a period of civil war where the very empire was said to have died, or almost died. They entered the "year of the four emperors." Finally Vespasian, at the urging of his troops, took the throne and the wound was healed.
Nero was the 5th head, who passed ending the Julio-Claudio Dynasty and leaving the empire to hang in the balance. Then we had 3 claim the throne in rapid succession in Galba, Otho and Vitellius, none of which lasted 9 months, each essentially being killed by their successor. We don't count those heads because they never received confirmation of the Senate and did not have public support.
The 6th was Vespasian "the beast which was" meaning John wrote Revelation between end of 69 AD and April 10 70 AD. Titus, the 7th, came to Jerusalem and stayed just 6 months before returning to Rome. Following the passing of Vespasian in 79 AD, Titus took the throne for only 2 years and 2 months, the shortest reign of all the heads. Then when Titus died in 81, the beast that was, and was not, returned in Domitian. Father and two sons all had the same name; Titus Flavius Caesar, the unholy trinity of the beast.