The size of the line-height is proportional to the font-size. Assuming you are currently using a unitless value for your line-height such as:
h1 {
line-height: 1.5;
}
You could try give it a pixel value instead.
h1 {
line-height: 30px;
}
Have you installed a new plugin or theme recently? If so, try deleting them to see if your site returns to normal. Problems in plugins can produce all kinds of weird problems and error messages.
