The Rolling Stones song "Bitch" is about doing heroin - specifically, a speedball mix of heroin and cocaine.
This is why the singer is "juiced up and sloppy" but "ain't touched a drink all night."
A HORSEmeat pie is a clear reference to heroin - which is also known as horse.
And finally, as any heroin user will tell you, the drug affects you differently on different occasions: Sometimes you'll feel "sexy, move like a stud / Kicking the stall all night and other times "so shy, got to be worked on / Don't have no bark or bite." (You might also be feeling "tired" and "distracted," notwithstanding having just had a "fortnight's sleep." - perfect descriptions of what it feels like sometimes after a Keith Richardsian drug binge.)
But EVERY time, the mere mention or thought of the drug will make you "salivate like a Pavlov dog," "You got to mix it child / Ya got to fix it," and, after a nice speedball, your heart WILL be "beating like a big bass drum."
I'm feeling so tired, can't understand it
Just had a fortnights sleep
I'm feeling so tired, Ow!, so distracted
Ain't touched a thing all week
I'm feelin' drunk, juiced up and sloppy
Ain't touched a drink all night
Feeling hungry, can't see the reason
Just had a horsemeat pie
Yeah when you call my name
I salivate like a Pavlov dog
Yeah when you lay me out
My heart starts beating like a big bass drum, alright
Yeah you got to mix it child
Ya got to fix it must be love
It's a bitch
You got to mix it child
Ya got to fix it must be love
It's a bitch allright
Sometimes I'm sexy, move like a stud
Kicking the stall all night
Sometimes I'm so shy, got to be worked on
Don't have no bark or bite
Yeah when you call my name
I salivate like a Pavlov dog
Yeah when you lay me out
My heart starts beating like a big bass drum