That's a really good question!
It could go either way, because when you think about it any feeling is actually an action of some kind: your stomach sinks, your heart races.
So when is an action a feeling and when is it a behaviour?
There's no precise answer, but we can consider whether an action is internal or external, and whether or not we have any direct control over it.
- Internal and no control: Our stomach churning or our heart thumping are actions inside ourselves, and we have no direct control over them, so they sound more like feelings than behaviours.
- External and some control: Exhaling or laughing or crying are external and we have direct control over whether we do them, so we might lean towards calling them behaviours.
- In between: Trembling is in-between; it's external but we don't have any control over it. So is it a behaviour or a feeling?
There's no right or wrong answer—it's a continuum!
What you should take from this discussion is the idea that feelings are both bodily sensations and experiences, but these are caused by actions within our bodies, and at some point they can become so big and explicit that we can start to think of them as behaviours.
Where you draw the line is up to you!