My ferret Dot (who is normally much less active) has been even more lethargic today and her belly feels very firm. I isolated her so I could monitor her food and water intake and poop. I gave her some Vaseline two hours ago and she has pooped once since (fairly normal). She does react to me and is up walking around, but her belly feels like a water balloon. She has only eaten a tiny bit of food in the past three hours. Should I give her more Vaseline? Do I need to take her to the vet first thing in the morning or am I overreacting?

For suspected blockages I give pure pumpkin and egg yolk. Since you've given Vaseline I would give some egg yolk. I use a small syringe and give about 4-5 syringes full. I would also get to the vet in the morning if things haven't changed. Blockages are an emergency and life threatening. Better safe than sorry. Keep us updated.

 
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I just gave her more Vaseline. She pooped again, but less this time :/ she has eaten literally four pieces of kibble in the past 4 hours :/ I did make sure she drank some water. Is there something else I should be doing? Do I need to wake up throughout the night? What does the egg yolk do? Do I give it totally raw or should I at least warm it first? Would it be ok to mix with a little soupie or wet food? Sorry for asking so many questions. I will get her to vet in the morning.

You said shes only eaten about 4 pieces of kibble. Are you feeding soupy too? I separate the yolk and white and put the yolk in a little cup. I don't warm it the first time. Left over goes in frig then warmed up when used again. I think it works better to just syringe it in by itself. I syringe the pure pumpkin in too. The egg yolk usually works pretty fast. Have you seen anything she might have chewed and swallowed? Or do you think it might be a hairball that finally got big enough to cause a problem? Since you're not even sure its a blockage i would get her to the vet ASAP. Could her spleen be enlarged? Ferret spleens are notorious for being enlarged at times. 

 
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If it is an enlarged spleen, what are some likely causes and what are the treatment options? And how much should I expect to pay for them? Is surgery on the table? How risky is a splenectomy? She doesn't seem to be pooping much at all though.

I've never had to have a spleen removed so I don't know. Lakota's would get huge but then go back down. While have had some through the years with enlarged spleens none were really a concern except his. 
Part of the reason for small poo can be less intake of food. When I suspected the blockage with Whiskers ( I found part of her blanket chewed) I gave the pumpkin/egg yolk and headed to the vet. On the way she pooped out a big piece of fleece. Took her on  in and they did an xray. Luckily she had pooped it all out. One other baby who I treated kept having problems and found out was a tumor in her intestines.
I would take her to vet.

 
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Ok. Thanks for the advice. I am taking her to the vet at noon (that was the earliest they could get me in). She is eating right now actually and is very alert so I'm feeling pretty good about that.

Any news?

THE DOOKS OF HAZARD

Sounds like a blockage to me. I would get him to the vet ASAP, ferrets with a blockage go downhill FAST

Nope, vet said there's no blockage and that it's probably swollen lymph nodes due to a minor infection. He prescribed a course of metro. It's all good. She had the first dose last night, but I didn't notice any difference in the swelling this morning, so I will post if I notice improvement.

good news.  hoping for the best

THE DOOKS OF HAZARD