This isn’t a case for endless investigation, which is its own problem. It’s a case for one adequate assessment, early, so that everything afterwards can proceed on solid ground.
It matters particularly if the anxiety appeared suddenly, appeared for the first time later in life, has no psychological context, or is predominantly physical.
The usual suspects
Thyroid. Hyperthyroidism produces palpitations, tremor, heat intolerance, weight loss, restlessness and insomnia — a near-perfect impersonation of an anxiety disorder. A simple blood test. This is the single most important one on the list.
Cardiac arrhythmias. Particularly supraventricular tachycardia, which causes sudden episodes of racing heart that stop abruptly, and is routinely diagnosed as panic disorder for years. If your episodes start and stop like a switch rather than building and fading, say so — a Holter monitor may be warranted.
Anaemia and B12 deficiency. Palpitations, breathlessness, fatigue, sometimes lightheadedness.
Blood sugar. Hypoglycaemia produces shakiness, sweating and a sense of dread. Worth considering if symptoms cluster before meals.
Sleep apnoea. Frequently presents as anxiety, fatigue and waking in a panic. Ask about it if you snore or wake unrefreshed.
Vestibular problems. Inner-ear disorders cause dizziness and unsteadiness that generate secondary anxiety, and get mislabelled.
Perimenopause. A very common and very under-recognised cause of new anxiety, palpitations and sleep disruption in the forties and fifties.
Rarely, phaeochromocytoma. A tumour producing adrenaline surges. Uncommon, and the classic triad of episodic headache, sweating and palpitations with high blood pressure is worth knowing about.
Medications and substances
Frequently overlooked. Salbutamol and other bronchodilators. Corticosteroids. Thyroid replacement at too high a dose. Decongestants. Stimulants for ADHD. Some antidepressants during the first fortnight. Withdrawal from benzodiazepines, alcohol, or an SSRI stopped abruptly.
And caffeine, in doses people don’t count — including pre-workout supplements, which are frequently 300mg or more.
What a reasonable workup looks like
Thyroid function, full blood count, B12 and ferritin, glucose or HbA1c, and an ECG. Add a Holter monitor if episodes are abrupt and paroxysmal. That’s a proportionate assessment for most people, and it’s reasonable to ask for it.
Then stop
Once a proper workup is clear, further investigation stops being diligence and becomes reassurance seeking — with the same four-minute half-life and the same tendency to grow.
The way to hold that line is to agree it with a doctor in advance: what routine follow-up looks like, and what would count as a genuinely new symptom. Set once, when calm, and not renegotiated during a spike.