to be sick
The Spanish phrase 'estar enfermo' translates to 'to be sick' in English. 'Estar' is a verb that means 'to be' and is used to denote temporary states or conditions. 'Enfermo' is an adjective that means 'sick'. This phrase is used to express the current health condition of a person which may change over time. One might say 'Yo estoy enfermo' to convey 'I am sick'. Remember, 'estar' is used for transient states of being unlike 'ser' which is used for permanent states and intrinsic qualities.
I think I'm going to be sick tomorrow.
This phrase expresses a future condition of health. The speaker suspects that they might fall ill the following day. The term 'estar enfermo' here is used to indicate a temporary state, as sickness is typically not a permanent condition.
I can't go to the cinema, I'm sick.
In this phrase, 'estar enfermo' is used to explain the speaker's current health condition, and it's the reason why they cannot go to the cinema. Again, 'estar enfermo' refers to a temporary state of being.
Since he decided not to get vaccinated, Juan seems to be sick all the time.
In this example, 'estar enfermo' is used to describe a frequent or recurring state of illness. The phrase highlights a recurring state of sickness might be causing the person's continual appearance of being unwell.