how do I stop this from happening

this happens every time I'm on my period and I don't know how to stop it. when I go to sleep I use a pad since I usually sleep more than 8 hours and I shouldn't wear a tampon that long. but when I wake up there will be no blood on my bed or shorts, but when I stand up gravity takes place and holy shit the amount of blood that comes out at once... by the time I'm in the bathroom my underwear and shorts are just covered in blood and it's just a mess. does anyone else have that problem? how can I stop that from happening?