"allez" is used here as an interjection. From Larousse :

allez !

interjection

Exprime l’encouragement, l’affection, la menace, etc. : Allez ! on se retrouvera.

It would be translated as come on! ("Come on, get up")

Should you want to use aller, a possible sentence could have been:

« Vas-y, debout ! »

or even, as allez as already stated is an interjection here:

« Allez, vas-y, debout ! »

Va alone is too literary to be used in that context but can be found in this famous verse:

« Va, cours, vole et nous venge ! »
– Corneille, le Cid