It is controversial whether emotions have rationality constraints or not.

It is controversial what emotions are...

I'm fairly fond of a view of emotions that has been championed by the empirically minded philosopher Jesse Prinz. According to Prinz:

Emotions are brain states that register bodily changes and represent core relational themes.

(I'm tempted to replace 'register' with 'represent' but that is a technicality, I guess).

For example: Fear is a certain kind of neural state that registers certain bodily changes (racing heart, eye dialation etc). The neural state also represents the relational property of something being a threat.

But of course you could jump at a garden hose or you could jump at a poisonous snake. Your amygdala can't discriminate the two so in one sense it is perfectly rational (makes good evolutionary sense) that there be a 'false positive'. But in another sense it is irrational to represent that a garden hose poses a threat to you because garden hoses are harmless.

Similarly... Sometimes we represent the world as being a certain way (e.g., someone intends to harm us or poses a threat to us, someone intends to insult us or demean us in some way). If the world turns out not to be that way (we misrepresented) then there is a sense in which our emotion could be said to be irrational.

But then given the life experiences some people have had (where people often intended to harm or belittle) it would make sense for a person to be wired up to be quick to represent the world in that way such that they can respond quickly (like how we are wired up to jump at garden hoses). So... Some people are hesitant to call this process 'rational' and instead they say it is 'understandable'. Whatever whatever (I think) lets not get caught up in a verbal dispute over the appropriate usage of the term 'rational'.