Unfortunately, without the additional information requested in my first/previous response, I will not be able to give you detailed advice to your question, but I will be able to give you a general answer, which I hope will be of assistance. If you are able to supply the additional information later, please do so and I will then come back to you with a more detailed answer.
You have not said what they have done to allegedly cause a trigger of you pre existing mental health issues.
It is however very unlikely they will be able to be held liable for that. If you have underlying mental health issues that could be triggered living in shared accommodation, then it could be argued that you should reside in sole tenancy accommodation and not be a possible burden on other tenants.
If your landlord has breach tenancy agreement there may be some recourse there, but again normally only to put right what has gone wrong.
Not everything that happens to someone can be sued, thankfully the U.K. has not reached that stage in live yet.
Therefore, if you think the landlord has done something wrong, you need to take a good look at the tenancy agreement to see where it fits in and what his responsibility is for it.
I hope that helps.
Thank you for using Just Answer and for allowing me to assist you with your legal enquiry. I am pleased I was able to be of assistance. Please do not hesitate to come back to me for further advice on this or any other legal matter. It will be my pleasure to be able to assist you again.