Yes, I have the same reaction, but also actual erections come about
while sleeping.  My theory is that there is a continual irritation
during PVP recovery which raises the level of stimulation just below
erection.  Then, when anything else comes along, (dreams, visual, or
just ordinary movement that is enough to bring about an erection.

My uro suggested 4 weeks abstention, which seems about right for me.

Viagra and Prostate Cancer (ED treatments, erectile dysfunction and prostate)

Men with prostate cancer who have their prostate removed are usually free of
cancer, but the procedure often comes with a cost -- impotence. A new study,
however, shows that Viagra (sildenafil), the popular medication for erectile
dysfunction, can restore impotency lost in surgery. Whether men respond,
however, depends on how much nerve damage occurred during surgery.
Each year some 200,000 men are diagnosed with prostate cancer and, of those,
50,000 will have to undergo surgical removal of the prostate.

"Incontinence and impotence are the two most common [prostatectomy] side
effects. A large number of patients, even with nerve-sparing techniques, end
up with erectile dysfunction," Milton Lakin, MD, who leads the medical
urology section at Cleveland Clinic Foundation, tells WebMD. "The first thing
[doctors] want to do is a very good cancer operation. Cancers are being
discovered early enough that in many cases it is possible to spare both
nerves, or at least one."

The new study, which appears in the November Journal of Urology, was
completed by physicians at Baylor College of Medicine in Houston. It involved
about 80 men who ranged in age from 47 to 76 years old. All were prescribed
Viagra following prostate removal surgery. Based on their responses to a
series of questionnaires, 53% had improved erections and 40% had improved
ability to have intercourse.

Among those with nerves spared on both sides of the prostate, almost 60% had
improved erections and about 45% reported improvement in their ability to
have intercourse. Of men who had nerves spared on one side of the prostate,
close to 40% had improvement of their ability to have intercourse. For men
with no nerves spared, the reported increase in erections dropped to 20%,
with only 10% noting an improvement in the ability to have intercourse.

At least one side effect each was experienced by 63% of the men, most
commonly flushing, headache, nasal congestion, and heartburn.

Brian Miles, MD, one of the study authors, called the results "gratifying"
and noted that the findings indicate patients should start on the medication
about six months after surgery. He tells WebMD that he has had success with
nerve transfers that involve implanting a leg nerve in the pelvis, which can
help maintain normal erectile function.

These findings confirm previous study results and put a greater spotlight on
the prostate surgery itself, says Lakin, who was not involved in this study
but has been part of nearly identical studies that produced similar results.
"I am not a surgeon. I deal primarily with sexual dysfunction. But where I
think this [study] will have the most impact is in causing physicians to pay
more attention to nerve sparing," he says.

Lakin says that he commonly prescribes Viagra following surgery for prostate
cancer because other options are more invasive. "Unfortunately, it's very
hard not to offer a patient a pill even if their nerves have been cut, but I
am very honest with them. And if they call and say it didn't work, we go on
from there."

If Viagra fails, physicians can recommend other options, including injections
and vacuum devices, both of which have good success rates, even among men
whose nerves were damaged, according to Lakin.

Vital Information:

Viagra is an effective treatment for impotency in men who have their prostate
removed.
For men whose nerves have been spared, the drug improves the ability to have
an erection by nearly 60%, but the effectiveness drops to 20% in those with
no nerves spared.
There are other options for men who don't respond to Viagra, including
injections and vacuum devices.

Generic Viagra costs 80% less
http://www.mensgenerics.com/viagra.php

I will not forget my first week with my second PVP. I had erections while
sleeping and I would almost come off the bed it would throb so bad. That only
last a week and two and went away.