I'm not seeing this. Two possibilities spring to mind (not likly a heat issue or the like as a reboot solves it):
1) Most likely, you have a bad app that is causing a memory leak or something. Remove third party apps one at a time until you find the blighter, or take a look at which app is draining up all the battery power in case that is an indicator.
[Seriously Sony? You're censoring the word 5ucking? Good grief, why? Anyone snowflake enough to freak out over such normal language would struggle hard when encountering a boiled sweet, not to mention the breakdown their encountering a vaccum cleaner would cause. Such people are beyond help, stop trying.]
2) Possibly your OS has gone wrong. Reset to factory defaults. If that fails, use the Sony utility mentioned on these forums to repairflash your phone with the current version of the OS.
One additional point, I hear some bad SD cards can cause slowness. Take your SD card out if you have one and see if the issue persists.
