Yes absolutely. I was speaking in a general sense.
Because being signed off with stress so frequently immediately follows something like performance management/disciplinary, there can be two problems. Firstly it is less likely to be taken seriously as an illness by some managers, sometimes leading to a lack of sympathy and support.
Secondly, because the assumption is often made by managers that the person in question has gone off with stress (either genuine or otherwise) because of the performance management/disciplinary, any other (possibly more significant and long-term) causes of the stress are sometimes not investigated and appropriate support is sometimes not given. This means the other, deeper problems are not taken into account when dealing with the performance problem.
It's really important that if your performance is being managed, any contributory factors are known by all involved. You are likely to be given much more leeway and support if your manager/HR are aware that there are other issues which are impacting your performance.
You have written to HR already, which is good. Longer-term I think the goal should be to identify one (ideally nice, supportive) person in HR to be your regular contact. Keep in touch with that person, meet them if at all possible, off-site if that's better for you, and be as open as you feel you can about your problems, taking any support offered.
You also need to continue contact with your line manager. This is often more difficult, especially given the performance management issue, but if the HR person knows your manager he/she may be able to help you identify how best to do this.