Ok, so recently after playing guitar for short periods of time(45 mins roughly) , my left hand and wrist start to hurt - to the point where i cant move my fingers for about half and hour. I used to play about 5-6 hours a day(before this..) and my parents think i might be developing RSI(repetitive strain injury).

1. could this just hand cramps or RSI?
2. is there any way to stop myself from getting it/ make it better faster if i do end up with it?, because i'm told i wouldn't be able to play guitar for at least 6 months if i do have it.

"The mind is its own place, and in itself

Can make a Heav'n of Hell, a Hell of Heav'n"

- John Milton, Paradise Lost
rub your hands before you play to get the blood flowing, dont exert yourself until you have warmed up playing
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Your neck may be too low and your having to bend your wrist more so just tighten up the srap.
i'd tap that .........speaking to a bass, its a music joke!

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Probably because you tore the crap out of your hand muscles playing for 6 hours, jeez take a break sometime. Try playing for say half an hour at a time, multiple times throughout the day