This is the 2644th most frequent Spanish word.
dormir
To sleep.
Here, 'dormí' is used in the past tense (first person singular) to describe an event that took place.
Ayer dormí muy bien después de un largo día.
Yesterday, I slept very well after a long day.
'Dormir' is in the infinitive form here, used to describe the act or intention of sleeping as part of a regular routine.
Siempre trato de dormir al menos ocho horas cada noche.
I always try to sleep at least eight hours each night.
In this case, 'dormir' is in the present tense (infinitive in the question structure), discussing the ability/inability to sleep currently.