Severe trouble breathing means:

• You cannot talk at all.
• You have to work very hard to breathe.
• You feel like you can't get enough air.
• You do not feel alert or cannot think clearly.

Moderate trouble breathing means:

• It's hard to talk in full sentences.
• It's hard to breathe with activity.

Mild trouble breathing means:

• You feel a little out of breath but can still talk.
• It's becoming hard to breathe with activity.