* Urinating less than usual
* Confusion
* Fast heart rate
* Pale and/or cold skin
* Thirst
* Generalized weakness

Visible signs of internal bleeding include:

* Blood in the urine
* Dark black stools
* Bright red stools
* Bloody noses
* Bruising
* Throwing up blood

Of note, it is possible to have internal bleeding without any of the above symptoms, and pain may or may not be present.

A patient may lose more than 30% of their blood volume before there are changes