Why is my mood so low?
Not a diagnosis: a head start. These are the three drivers most worth checking first, based on what the evidence says gets missed most often.
Biology first, always
Vitamin D, B12, thyroid, iron and inflammation all produce low mood and are all testable.
Sleep debt compounds
Mood and sleep drive each other. Fix the sleep half and the mood half lightens.
Weeks, not days
A low patch lasting weeks is a GP conversation in itself. That is not weakness; it is data.
Vitamin D, B12, TSH, ferritin, HbA1c
1. Start a two-minute note so the pattern becomes visible.
2. Take the test list above with you so you can explain the pattern clearly.
3. Read the evidence: Low Mood vs Depression: When Sadness Is Something More · Vitamin D Deficiency UK: Why 90% Are Low and What It Actually Does.
Education, not diagnosis, and never a replacement for your GP or pharmacist. Reference ranges and guidance vary; sudden, severe or worsening symptoms need 111, or 999 in an emergency. By Hussain Sharifi · independent, affiliate-free health research.