I'm worried
Use this to say 'It worries me...' when you want to specify the cause of your worry immediately. It's very common.
Means 'I'm uneasy' or 'I'm restless'. Use this for a feeling of anxiety or agitation, not necessarily a specific, defined worry.
Literally 'I have a worry'. This frames the worry as a noun, something you possess. It's a slightly more formal or detached way to express it.
I'm worried about tomorrow's test.
My mom is worried because I'm not arriving home.
The situation worries me a lot.
Why are you so uneasy? Did something happen?
It's nothing, I just have a small worry about the trip.
The verb 'preocupar' is standard across the entire Spanish-speaking world. The key is remembering to use 'estar' for the temporary feeling ('Estoy preocupado') and to match the gender ('preocupado' for men, 'preocupada' for women).
Completely standard. You might also hear 'andar preocupado/a', which means something like 'to be going around worried', emphasizing the ongoing nature of the feeling.
The phrase is the same, but the pronunciation of 'Estoy' will sound more like 'esh-TOY' due to the characteristic 'yeísmo rehilado' accent.
No significant difference in meaning or usage. 'Estoy preocupado/a' is the standard expression.
Using 'ser' instead of 'estar'. Saying 'Soy preocupado' means 'I am a worried person' (a personality trait), not 'I am worried right now' (a temporary state). — Always use 'estar' for current feelings: 'Estoy preocupado/a'.
Forgetting to change the ending for gender. An English speaker might say 'Mi hermana está preocupado'. — The adjective must match the gender of the person: 'Mi hermana está preocupada'.
Using the wrong preposition. Learners often say 'Estoy preocupado con...' or '...para...'. — The correct preposition to introduce the cause of worry is almost always 'por'. For example, 'Estoy preocupado por ti' (I'm worried about you).