In what way do they fall on the same axis? These do capture two of the three main options ancient medicine saw in mental disease: mania, catatonic melancholy, and dementia precox, as surveyed by Krepelin early in the history of modern psychology. Excessive euphoria is by definition manic and Paranoia is often schizophrenic (which is the disease that was seen as premature dementia -- like senile dementia but with the energy of youth, and therefore dangerous to others.)
But we no longer see thing this way. We think these problems were seen as primary in Classical systems simply because they were the most dangerous to others, not because they were in some sense more basic diseases.
From modern personality theory, we think they are independent and lie on no common axis.
The most common set of independent factors in vocabularies of personality are the Big-5 set: Openness to new experience, attention to Conscience, Extraversion, tendency to seek Agreement, and Negativity/Neurosis or tendency to question purposes.
From that perspective the totality of Aristotle's 'courage' is a segmentation of the axis of 'openness to new experience' into three ranges: lack of respect for known patterns (recklessness), genuine willingness to risk (courage), and fear of unknown outcomes (cowardice).
Paranoia may look like a character trait, but it is mostly an aspect of psychosis. It arises primarily from unrestrained intuitive information gathering when one's ability to collate information changes unexpectedly. When one is unconsciously aware that one's grasp of reality is changing, the mind obsessively seeks patterns to give reality a sense of solidity. One is also afraid, both consciously and unconsciously, so there is a bias toward those obsessive patterns being made up of objective things to be afraid of.
People do not tend to change characterologically when they become paranoid. They attend obsessively to correlating facts into a threats. But they may then address these delusional threats boldly, timorously, or recklessly, as they would address genuine threats.
Euphoria is no longer seen as something people have in isolation. It is a passing state which is part of a tendency toward breadth of mood (bipolarity) -- no one is characterologically euphoric without also being severely depressed. Breadth of mood itself is part of the Negativity axis. To vastly oversimplify, when one is habitually conflicted and uncertain, one responds alternately with fear and anger at the outside world for its lack of reassurance, which makes one artificially certain, and with disgust at ones own lack of intelligence or fiber in not being able to make stable decisions.
So I don't see this axis, and neither does most statistical analysis of language used to describe other people, or observed trends in people's styles of functioning.