Ok, some of them might coincidentally be true, but a thought itself is not necessarily true. Just because we have a thought, doesn't make it true.
This is true generally but especially true related to depressed or suicidal thoughts, so that's where I'll focus today, in reviewing some of the recent relevant research, but it's true generally as well. We don't entirely know where thoughts come from, so why completely believe them?
A bundle of interesting studies recently has highlighted the role of pollen in increasing suicidal behavior, with specific studies looking at differences by gender (significant risk for females, not males) and type of pollen (tree or grass increases risk but not ragweed), history of mood disorders (if you haven't had depression/anxiety, allergens increase the risk, if you have allergens reduce the risk), and effects of accounting for sunlight exposure (sunlight doesn't account for differences in risk). There has also been research on how different allergy medications affect risk for suicide (antihistamines increase risk but intranasal corticosteroids lower risk, regardless of psychiatric medications).
There are a number of different possible reasons for this, and Much more research is necessary to really figure out what's going on. There's certainly not enough research to suggest that any particular lifestyle change; however, it does support the case that the thoughts that might come to mind (e. g. "I should kill myself") may not be based on any kind of fact-based information. This is also consistent with research on how bacteria in your gut can affect your mood and thinking. Some thoughts may be a reaction or interpretation of different stress responses in your system.
Our brains take in all kinds of information, internally (from your gut, pain sensations, level of exhaustion, and hunger, for example) and externally (how people interact with you, whether we feel like we are a positive contributor or a burden to those around us, for example). Then the brain pulls them together into something that can take the form of coherent thought.
That "pulling together" however, might not be totally accurate. It might be an disproportionate reaction, only based on one angle of information (only the negative, for example), might neglect to also suggest all the other ways of interpreting the incoming information, and so on.
It is up to us to take a step back from our thoughts and take a second look when they are unhelpful or disproportionate to the situation. Where did this thought come from? Is it based on fact, on feelings, or fact-based feelings? What other information might be helpful?
An every-day-life application of this might be -- if you're over-stressed and burnt out at work, you might think "I can't handle my job," "I can't meet my boss's expectations, so there must be something wrong with me/I'm a failure," "I'm never going to be able to be successful at this." All of these are examples of thoughts that be coming from internal signals of stress and exhaustion rather than based on actual performance. They might be coming from external signals of the stress or personalities within those around you. They might be coming from a larger system of unrealistic expectations and pressure, or a simple mismatch in training and position or expectations and reality. Thoughts like those above might benefit from a second look because they are unhelpful and very likely are distortions or misrepresentations of things you have come to believe as complete truths but are actually not (don't get defensive -- it's totally normal and human).
When we see thoughts for what they are -- just thoughts -- it empowers us to decide which thoughts are most helpful and most life-giving, and, over time, craft a more stable and fruitful life.