I startle and jerk all through the night in my sleep. It wakes me sometimes and disturbs my husband. Could it be a side effect of effexor (venlafaxine)?

NIghttime jerking. In the clinical trials with effexor, (venlafaxine) a small group (1%-3%) of patients had twitching muscles. Some (5%) had tremor. Some also had hyper-reflexia and CNS stimulation -- which could possibly contribute to what you're experiencing. Did you have a strong startle reflex before starting the medicine? If you're dreaming intensely, this could be affecting things also. Talk with your doctor about this.
It is possible. Anxiety, nervousness, tremor and abnormal dreams are fairly common side effects . It is possible that the Effexor (venlafaxine) is causing the symptoms described. The only way to be sure would be to reduce the dosage or safely stop the medication. This should only be done in consultation with the treating physician. It is possible that other medications or combinations of drugs could be the problem.
Depends. If you recently started taken Effexor (venlafaxine) before onset of these sxs, it may be wise to talk to your doctor about it as people respond differently to medications. However, if your sxs are not related to the use of effexor, (venlafaxine) you may benefit from an evaluation to investigate the sxs further and rule out conditions like restless leg syndrome and other sleep disorder related problems.
Could be. If the Effexor (venlafaxine) is not required, it would be reasonable to stop the med and see what happens. This could also be periodic leg movement disorder or sleep apnea. If this persists you may need a polysomnogram.
Yes. Quite possible. This medication has probably the highest likelihood of of any commonly used mood stabilizer of promoting limb movements of sleep.