My GI told me I didn't have to go to the ER unless the pain and nausea were unbearable. I would avoid it if at all possible. After my colectomy I had a kink in my bowel that prevented me from eating any solids for five weeks till my takedown--otherwise I'd get obstructed. It was awful. I survived on Ensure, chicken broth, and V8 till he did the takedown and adhesion lysis. 

Not all obstructions require an ER visit, but there are at least three things they can offer: 1)  if you're unable to get any fluid through, an IV can help keep you from becoming dehydrated. 2) if things get very bad, and there's concern about a bowel rupture, you should be in or near an operating room. 3) sometimes an NG tube can relieve some of the pressure.

 

I would avoid opiate pain medication for an obstruction, as tempting as it is.

I've only had one obstruction and it was caused by a twisted small intestine.  Morphine was my Godsend!  I don't think I would have made it without.  My surgeon kept me in the hospital 6 days.  Each time he visited he manipulated my abdomen.  I never asked why and wondered what he was feeling for!  Well, he worked a miracle by untwisting my bowel this way! It took four days.  I am so thankful he avoided surgery and his technique worked.

Unfortunately I don't think most surgeons will take the time to gently help the bowel untwist. One of the natural forces that can help is ordinary peristalsis working to (and hopefully past) the kink. Reducing that peristalsis with opiates could slow the resolution of the obstruction, though I don't know if it's been studied carefully. In some cases the opiates may be needed to help keep you from chewing your own arm off, but they could also make it harder to tell if a bowel rupture is imminent. Sometimes there are no great choices.

I had one obstruction that put me in surgery. 
I have had three but o ly this one got bad.
They couldn't find it after ten hours of digging around.
I had an illeo then and they were looking all over. 
The pain was so intense.  I had to have painkillers.  Thru a port.
Omg I have never felt pain so bad in my life.  Morphine would ot even take the pain away.  Then they tried demerol.  I could relax finally.  But it didn't last long and the pain was back.  Sometimes you just have to have the relief.  It was terrible and burned in my memory. 
I was told by one woman... Who had a blockage and she compared it to childbirth.  I am a male but if it is like that I would dread having a baby if I were a female.
Thing about it was the blockage was right by my stoma.  And they dug for an hour there looking for it effort they cut on me.
And yes... A ng tube was a huge relief also.  I still had so much in my stomach they couldn't believe it.  I never want to go through that again.