The physical conditions that get mistaken for anxiety

A racing heart, a knot in your stomach, sleep that will not come, a mind that will not settle. Every one of those can be anxiety. They can also be a thyroid gland working too hard, or a blood count running low. The two sets of symptoms overlap closely enough that telling them apart from the inside is genuinely difficult, which is exactly why it is worth a blood test looking rather than you guessing.

The short version

• An overactive thyroid, medically called hyperthyroidism, lists nervousness, anxiety and irritability among its common symptoms, alongside a racing heart, sweating and unexplained weight loss.
• Anaemia, whether from low iron or low vitamin B12, can produce palpitations, breathlessness and tiredness, and low B12 specifically can cause anxiety as one of its own listed symptoms.
• Both are checked with a simple blood test, which generalised anxiety disorder (GAD) does not require for its own diagnosis.
• If your anxiety symptoms are new, sudden, or not settling the way you would expect, asking your GP for a blood test is a reasonable next step, not an overreaction.

A diagnosis with no test attached

One thing is worth being clear about first. Generalised anxiety disorder is diagnosed by talking, not by blood. The NHS describes a GP asking about your worries and physical symptoms, then diagnosing GAD where you worry about a wide range of things, it is affecting your daily life, it is hard to control, and it has gone on for at least six months. There is no blood test built into that criteria, and nothing in it distinguishes worry driven by your circumstances from worry driven by a gland or an organ that is not working quite right. That is not a flaw in how anxiety gets diagnosed. It is a reason the physical possibilities need to be checked, not assumed away because the pattern fits.

The thyroid working too hard

An overactive thyroid pushes out more thyroid hormone than your body needs, which speeds nearly everything up. The NHS lists nervousness, anxiety and irritability as common symptoms, sitting alongside a fast or irregular heartbeat, trouble sleeping, feeling hot, sweating, trembling, and losing weight despite an increased appetite. Some people also notice a swelling at the front of the neck. On its own, any one of these could be anxiety having a bad week. Together, especially the heat intolerance and the weight loss, they point somewhere more specific.

The overlap runs the other way too: plenty of people with a genuinely overactive thyroid spend months believing they are simply anxious, because the two feel so alike from the inside.

The usual cause is Graves' disease, an autoimmune condition, though thyroid nodules or certain medicines can also be responsible. A GP arranges a blood test to check the thyroid, and treatment (medication, radioactive iodine, or occasionally surgery) is guided by an endocrinologist once the cause is clear. In my experience it is a satisfying diagnosis to make, because the fix is usually straightforward once found.

Low iron, low B12

Anaemia means your blood is not carrying enough oxygen around your body, and the two common causes worth knowing about here are low iron and low vitamin B12 or folate. Iron deficiency anaemia commonly causes tiredness, breathlessness, noticeable heartbeats, and headaches. Vitamin B12 or folate deficiency anaemia can bring rapid breathing, palpitations, pins and needles, a sore tongue, and, the NHS notes, psychological problems that can range from mild depression or anxiety to confusion and dementia. Iron deficiency anaemia is diagnosed with a full blood count (FBC), a standard blood test that looks at your red blood cells. B12 and folate deficiency is diagnosed the same way, plus a direct measure of B12 and folate levels in your blood; the NHS is upfront that some people have symptoms with normal levels, and some have low levels with no symptoms, so a GP weighs the blood result alongside how you are actually feeling.

What about your heart itself

A heart that skips, flutters or races for no obvious reason can also be an arrhythmia, a rhythm problem in its own right rather than a symptom of anxiety or of anaemia and thyroid trouble. We have covered that ground properly in heart palpitations and when to get them checked, so this is the short version: if palpitations come with chest pain, breathlessness, or fainting, that needs urgent same-day attention, not a wait-and-see. The NHS is specific about this: call 999 or go to A&E if palpitations do not settle alongside any of those. If they keep recurring, last more than a few minutes, or you have a known heart condition, that is a GP appointment rather than an emergency.

What a GP actually checks first

None of this needs anything exotic. Working through new or unexplained anxiety-type symptoms typically starts with a thyroid blood test and a full blood count, since both are quick, cheap and already routine, with B12 and folate levels often added in the same round. Alongside that, expect questions about caffeine and alcohol, which can produce a near-identical racing feeling of their own, and about any medicines you take, since some carry anxiety-like side effects. Bloods are one part of the appointment, not a replacement for the rest of it.

In my experience, most people who get checked this way do have anxiety, plain and simple, and the tests come back clear. That is not a wasted trip. Ruling out a treatable physical cause first is what makes the anxiety diagnosis that follows one you can trust, rather than one reached by default because nobody looked for anything else.

If everything comes back clear

A clear blood test does not settle the question of what to do about the anxiety, only what it is not. Therapy is still worth considering, and one shape worth knowing about is brightloaf's, where sessions run twenty minutes rather than the standard fifty. That is a decision about length and only length, not a claim about what any given length achieves. The reasoning is set out in can 20 minutes actually help.

If you ever have chest pain, breathlessness, or feel faint alongside a racing heart, treat that as urgent and call 999 or go to A&E rather than waiting to see a GP. This article is not a substitute for personal medical advice: only a blood test and a conversation with your GP can tell you which of these explanations, if any, fits what you are feeling.