I wouldn't worry, (I know that's easy to say) but it will most probably grow back

Does any of this sound familiar

Telogen effluvium
Telogen effluvium is a common type of alopecia where there is widespread thinning of the hair, rather than specific bald patches. Your hair may feel thinner, but you're unlikely to lose it all and your other body hair isn't usually affected.

Telogen effluvium can be caused by your body reacting to:

Hormonal changes, such as those that take place when a woman is pregnant
Intense emotional stress
Intense physical stress, such as childbirth
A short-term illness, such as a severe infection or an operation
A long-term illness, such as cancer or liver disease
Changes in your diet, such as crash-dieting
Some medications, such as anticoagulants (medicines that reduce the ability of your blood to clot) or beta-blockers (used to treat a number of conditions, such as high blood pressure)

In most cases of telogen effluvium, your hair will stop falling out and start to grow back within six months.