Following this year's horrific terror attacks in London and Manchester, many families used social media to try to find missing loved ones, as well as to share their incredibly traumatic experiences.
Recognising the role that social media can play after a terror attack, NHS England is issuing new guidance to staff and victims warning them to use their accounts cautiously.
The new guidance advises staff and victims to be especially wary of journalists, whose tweeted questions can be "seductive" as well as "very intrusive, and sometimes blunt."
It also specifically warns younger victims about online trolls who "draw the most negative conclusions they can, or question your motives that don't exist, or just [become] plainly unpleasant and abusive."
The guidance says of trolls: "They can say things like you're only doing something for money or to abuse the system and so on. This is incredibly hurtful - which is what the sender intends - and it will upset you, or make you angry, and that's never the best time to think about what you tell."
The guidance advises people who are targeted by trolls not to respond to their hateful messages, and to block them wherever possible. "Consider reporting hateful and abusive messages to the police and service providers," it adds. "Tell a family member or a close trusted friend who's a good listener about it and how it made you feel."
Although the NHS England guidance acknowledges that the "advantages of social media outweigh the disadvantages", it still advises victims to "try to stay off social media in case you say more than you intend because of what you experienced."
It adds: "Messaging your story can keep you in the trauma; retelling your story can also bring back bad memories and you can even relive the trauma."
The new guidance has been broadly welcomed by Dan Hett, whose brother Martyn Hett was one of the 22 people tragically killed in the Manchester terror attack. He told the BBC: "Overall I'm very much in favour of clear guidance being put in place for people, but to be honest I think some basic decency should really cover most of it."