Fear is corrosive. It's contagious. Fear impedes your ability to think straight. It skews your perceptions of risk. At its worst, it can paralyse you completely. Right now, fear is all around us: in the shocking headlines, in the death counts, in the near-silent queues of people waiting to get into the supermarket. We're breathing it in constantly.
So it should come as no surprise that the mental health of the population is suffering.
The Royal College of Psychiatrists (RCP) reports that people with no previous history of mental illness are developing serious psychological problems for the first time, as a result of the coronavirus crisis.
Adults and children are experiencing symptoms of serious mood disorders such as mania, depression and psychotic episodes, triggered both by the pandemic itself and by the lockdown response. Young men, aged 18 to 25, are especially affected by first-time mental health issues.
Fear of illness, fear of recession, unemployment, bereavement, isolation, absence of normal routines, relationship pressures heightened by being cooped up at home for weeks on end.
Add a dash of acute insomnia, and you've got the toxic cocktail that is tipping many people into appalling distress.
The fact that more than half a million people accessed an online suicide prevention programme in the last three weeks alone speaks for itself.
While it's bad enough now, this largely hidden epidemic is only going to get worse.
Mental health experts are expecting a dramatic upsurge of people needing treatment once the lockdown restrictions are eased. The RCP warns that services could be overwhelmed by "a tsunami of mental illness".
Why? Well, when they are in the middle of a crisis, many people are able to cope, fuelled by adrenaline, social solidarity and a sense of purpose. All their focus is on getting through.
It's only when the threat passes that the damage becomes clear - and that's when things start to fall apart.
Frontline healthcare workers, directly exposed to the worst cases of Covid-19, are thought to be at particular risk of post-traumatic stress disorder, a horribly debilitating condition.
Here in Northern Ireland, the situation is especially acute because we have a society that is already ravaged by the trauma of the Troubles. We were in no shape to take yet more emotional pain, and yet we have.
So the announcement, by the Health Minister Robin Swann, of a new action plan to improve mental health services is a welcome one, as is Mr Swann's acknowledgement that mental health issues "are going to be one of the biggest fall-outs" from the pandemic.
Yet a plan is just a plan: what we really need is fully-funded, coordinated action, and urgently.
We also need to reflect on the role that governments themselves played in stoking public fears as a means of ensuring widespread compliance with the restrictions.
Professor Robert Dingwall, an adviser to SAGE, the UK government's scientific emergency group, said that the population has been "effectively terrorised" into believing they will die if they catch coronavirus, thus creating a "climate of fear" in which people are now too scared to return to their daily lives.
Professor Dingwall added that Britain had "completely lost sight" of the true nature of the disease, which for the majority of people is relatively mild. A SAGE discussion paper from March 22, entitled 'Options for increasing adherence to social distancing measures', gives weight to Prof Dingwall's analysis.
The paper speaks of increasing the "perceived level of personal threat" posed by the virus, by using "hard-hitting emotional messaging".
Was this what our own Mr Swann was trying to do when he warned of "a surge of Biblical proportions", claiming that 15,000 people could die in Northern Ireland?
In my view, it is morally unjustifiable to play on people's basic survival fears as an instrument of public control.
It is possible to explain the serious nature of a threat such as Covid-19, to identify those most at risk, and to emphasise the vital need for compliance with social distancing measures, without resorting to overblown scare tactics.
Given what we know now about the precarious state of the nation's mental health, such state-sanctioned forms of emotional blackmail are even harder to defend.
Fear is a powerful but crude tool. The government's apocalyptic messaging has been so effective that many people are too frightened to seek emergency medical treatment or to send their children back to school.
Professor Karol Sikora, the renowned oncologist, has warned that when the history books are written, this fear will be seen to have done much more damage than the virus itself.
Lessons for the future must be learned now.