A sample sentence would be:
I have this lingering feeling of [irrational doubt] that's discouraging me from pursuing my goals.
I've used Merriam Webster to search for synonyms for doubt but none appeared to be what I was looking for which are distrust, distrustfulness, dubiety, dubitation [archaic], incertitude, misdoubt, misgiving, mistrust, mistrustfulness, query, reservation, skepticism, suspicion, uncertainty. None of which includes the irrational part to it.
Compound word or phrase can be acceptable.