Two months after falling ill with Covid-19, Julie had her first hallucination. “It started slowly. I was struggling to track the plot of a TV show, then I couldn’t read the words on my phone screen,” she said.

Things deteriorated, with an overwhelming sense of her mind and body being consumed. “I know it sounds crazy, and I don’t know how to properly articulate it, but in the moment it really felt like something was taking over my brain and my body.

“I was so convinced that was happening that I made my sister promise to remember a code word so she’d know if I was still in my body.”

Amid these delusions, Julie, 36, from Minnesota, was eventually taken to hospital by her family. “My mom told the ER doctor that I was recovering from Covid and that they were concerned this was a strange side-effect. He agreed it was possible, but didn’t seem to have any treatment to suggest.”

Julie is not alone. As the long and lingering effects of Covid on physical health are emerging, so too are its impacts on mental health.

Research from Italy found that more than half of those admitted to hospital with Covid-19 had a psychiatric disorder a month later, with 28% showing signs of post-traumatic stress disorder (PTSD), 31% depression and 42% anxiety. Insomnia and obsessive-compulsive symptoms were also common.

A study by researchers at University College London (UCL) also flagged psychiatric and neurological problems following Covid infections. The husband of one woman discharged from hospital found her behaving oddly, taking her coat on and off repeatedly and saying she saw lions and monkeys in the house.

It is not only those ill enough to be admitted to hospital who are affected, as members of a Covid-19 group on the social media platform Slack, who include Julie, attest.

Before Covid struck, Dawn, 48, also a member of the Slack group, was an organ transplant coordinator in Philadelphia. Now she is unemployed, and on a recent visit to friends took half an hour to feel comfortable getting out of the car.

After Dawn was diagnosed with Covid, her anxieties about the disease grew. She experienced chest pains and panic attacks. “I would walk around the house [at night] and make sure everyone was breathing,” she said. In June, as her younger daughter became increasingly concerned and physical causes were ruled out, Dawn sought mental health services.

She has since been diagnosed with PTSD, generalised anxiety disorder and major depression, and is undergoing an intensive outpatient therapy programme. “I am two months into my therapy and … still having quite a difficult time getting out of my house,” she said.

Lauren Nichols, 32, from Boston, Massachusetts, said while isolation had taken its toll, she experienced “sheer fear” after the acute infection stage of Covid passed. “I was waking up in the middle of the night gasping for air,” she said, adding she was left terrified of sleeping and afraid of being unable to call out to her husband if she felt she was dying.

Protests against mask wearing, gaslighting by doctors and relapses have also affected her mental health. “Every time I have a relapse unfortunately it feels like day one of Covid,” she said. “I fear instantly that I have Covid again.”

Sophie, 25, from the south of England, had suspected Covid at the end of March and is afraid of catching the disease a second time. After the physical symptoms had passed, she was left with constant panic attacks that would seem to last the entire day.

“I have been diagnosed with a generalised anxiety disorder and am taking medication for this. I am still left really anxious and nervous that I will become unwell again,” she said. “I am only now feeling better, but still feel socially anxious and scared of going to public places.”

Dr Jonathan Rogers, a neuropsychiatrist at UCL and part of a team working on the mental health and neurological impacts of Covid-19, said much of the research had been carried out on patients in hospitals, rather than in the community. “It is a bit of a neglected group in terms of research, which is remarkable given that it is the vast majority of people with Covid,” he said.

Social isolation, stress, unemployment, difficulties getting back to work, ongoing fatigue and financial difficulties could all give rise to mental health problems in Covid survivors, he said, as well as the experience of being unwell or ending up in an environment like intensive care.

There are also factors more specific to Covid, including concerns about having infected others. “I saw patients in hospital who were objectively not that unwell and were getting better, but because of the panic about Covid, were convinced they were going to die. Even people saying “just kill me now doctor,” Rogers said.

Could Covid-19 be affecting the brain directly? Rogers notes there have been cases of brain inflammation, or encephalitis, linked to the disease, but says these are very rare.

The Italian study, however, suggested Covid patients with higher levels of markers of inflammation in the blood were more likely to develop depression and anxiety afterwards, he said.

Some might argue both arise because such patients are more unwell, but the alternative explanation would be that inflammatory substances are affecting the brain and causing psychiatric disorders, Rogers suggested.

Patients should be asked questions about their mood, anxiety, sleep and fatigue in routine follow-up appointments with GPs or respiratory teams, he said, with onward referral as necessary. Employers needed to show flexibility in helping Covid survivors return to work, he added.

Dr Nick Grey, a consultant clinical psychologist at Sussex Partnership NHS foundation trust and the University of Sussex, is part of a team of experts who have set up a Covid trauma response working group, which has developed clinical guidance for monitoring the mental health of patients who have had severe cases of the disease.

Among its recommendations, the guidance suggests screening the mental health of patients four weeks after discharge from hospital and offering “subsequent active monitoring assessments” every three months, at least for the first year.

The NHS has set up a website for people who have had Covid-19, Yourcovidrecovery.nhs.uk. “It provides links to getting appropriate local help both for physical and emotional needs,” Grey said.

Dawn said mental health support was crucial. “Everyone was telling me to get back to work, including my own husband, but I mentally couldn’t do it, and I can’t explain to other people why that is, until people tell me why I am having these feelings,” she said.

Nichols said she had put off seeking a mental health diagnosis or therapy because she was concerned that having it on her record might lead to symptoms of a second Covid infection being dismissed. She stressed, however, that it was important for those experiencing problems to know help was available, be it therapy or support groups.

“Fighting this alone, whether that be in isolation or feeling like there is [not] another soul who is really into what you are going through, it doesn’t have to be that way,” she said.