my psp shuts off sometimes while supposedly sleeping

[derp]

i am noticing lately that instead of sleeping my psp somehow manages to shut down completely and i find this pretty annoying because it makes me think that something is wrong with it.

does anyone know whats the major cause of this? it doesn't turn off or anything when i'm playing or using it but sometimes when i leave it idling and put it in sleep mode (switching the power button for a sec) and then an hour(s) or more passes before i touch it agan and so i flick the power back on and i hear the little sony startup melody

i wanna say it started happening when the psp fell but i'm not entirely sure that caused it so i am asking here for peace of mind, and as i said nothing is wrong with it otherwise it just doesn't stay sleeping like it should

[Demonchild]

Make sure that the battery isn't going dead or becoming disconnected from the unit. If so, it clears out the memory that sleep mode uses.