I don’t know when my depression started, and I also don’t know when it stopped. My first memory of feeling very low is an awkward conversation with one of my sixth form teachers. Pushing in my plastic stool as the class filed out, he pulled me aside for a chat. “Everything okay?” he asked, with a huge, sympathetic upward inflection. “You seem like you might be on a bit of a…” he blew a raspberry and gave a slapstick thumbs down, “…downer.”

I was on a bit of a downer, but I didn’t have the tools to understand that at the time, let alone know how to admit it to someone I considered a grown-up. I was 16 and spending afternoons huddled in the corner of the common room fulfilling the teenage Plath-reading stereotype, when I should have been in biology. When I was forced to go to lessons, I would sit in the back and do the bare minimum. I was not surviving well.

By university, instead of afternoons off it became whole days in bed – living away from home meant I could get away with it. I’d always been very anxious and often sad, but the feeling was mounting, and with first year exams hurtling towards me, I walked to the practice adjoined to my college and got a diagnosis. On the questionnaire my GP had peeled off of a stack in her desk drawer, I ticked a lot of answers that said “most of the time” and “not at all”. I got given a glossy leaflet to go home with, with the big word “depression” spelled out in sans serif.

Four years, one mental health crisis and many therapy sessions later, I am okay, often very good. But things aren’t the same. After having been there, sadness has a different significance. Is it part of the package of having dealt with a serious mental illness, of knowing of how bad it can get?

I’m aware this isn’t just me – societally we talk and think about mental health more than we used to. While being on the lookout for symptoms can be incredibly positive, for myself, and many of my friends, increased awareness can mean increased anxiety. Whenever I’m sad, alarm bells go off. I know sadness is a part of life, but it can feel like a dangerous omen when it pops up before bed, or on the train in the morning without warning. I worry a lot about what will happen if I lean into it. Without therapy or medication, sometimes being out in the world alone with your sadness is scary.

Diagnosis is an intensely medical concept – the rules that state who is and who isn’t “mentally ill” were invented by psychiatrists, and are tied to the idea of whether you can work. Rigid and stringent, diagnosis can barely scratch the surface of how complicated it really is; the diagnostic criteria for depression specifies that you have to experience your symptoms of low mood for two weeks or more, but nothing magical happens on day fourteen of feeling too low to get out of bed. Like much else in the way we shove mental health problems into boxes, it’s an arbitrary number decided on a scale. With this in mind, can sadness really be a completely distinct and separate entity?

We’re frequently reminded depression is “not just like feeling sad”. But having experienced both, I don’t think it should be taboo to admit that my sadness isn’t that different to what my depression was like. Sometimes I still go through periods of feeling very crap for a while. I can overthink something small so much that I can’t concentrate on work; but my net production is high enough that this generally goes unnoticed. During these periods, I’m probably not ill, but I’m not quite well.

This is why sadness can be scary. I don’t know when my depression started, and I also don’t know when it stopped. I don’t even know if thinking about it in that framework is necessarily helpful – mental health and illness have been a big part of my own life and identity, and my relationship to it is personal, intense, and ongoing. Whether my foot is over the line, or just outside of it, I can always see it. I am always thinking about it, and my relationship to it.

There’s no real inspiring takeaway. You could say that learning to “pull yourself up by your bootstraps” and deal with sadness without support is admirable, but I don’t believe that at all. I wish anyone could pop into the doctors or access short-term therapy on days when they feel like they’re flagging, rather than telling themselves they can always go on the waiting list if things get really bad. But in the current state of austerity, even those at crisis point can struggle to get support.

Another possible takeaway could be that there’s a clear difference between being mentally ill and healthy sadness – and that after the upward trajectory of recovery you gain the tools to stay above the clinical line. But that’s not true either, it’s possible to become ill again, and sometimes I think I probably will. Mental illness runs in my family, I am a black Caribbean woman, and I have a history of trauma – the statistical odds are stacked against me. Getting ill again at some point down the line seems unavoidable.

We can’t separate mental illness from the society that decided what counts in the first place, and it’s also not always possible to “fix” problems that are more complicated than a simple illness with a simple cure. But we can change the way that we think about it. Mental health problems don’t always just “start” and “stop” – they can be abstract, subjective, and in flux. Something about that is scary – a huge expanse suddenly blown wide open. But in some ways, it is also quite freeing.

Useful websites and helplines:

• Mind, open Monday to Friday, 9am-6pm on 0300 123 3393
• Samaritans offers a listening service which is open 24 hours a day, on 116 123 (UK and ROI – this number is FREE to call and will not appear on your phone bill.)
• The Mix is a free support service for people under 25. Call 0808 808 4994 or email: help@themix.org.uk
• Rethink Mental Illness offers practical help through its advice line which can be reached on 0300 5000 927 (open Monday to Friday 10am-4pm). More info can be found on www.rethink.org.