Please help - older dog acting strange, walking slowly, unbalanced, drinking lots

Hi

I was wondering if anyone had had similar symptoms in one of their dogs who could offer advice. I really want to take her to the vet but its a lot of stress for her and I don't know if I am being paranoid.

This started 5 days ago, my 13 year old cross was not herself. During the night she became very ill, vomiting and drinking lots of water and repeating, whimpering when laying down like her stomach hurt. We thought maybe it was something she ate, she looked in pain when standing, she didn't know where to put herself and walked very slowly, just generally very fragile. She continued like this for the rest of the day, shivering on and off. The next day she improved slightly, we gave her some Chappy which she ate. She seemed to get better over the next couple of days, though not completely back to normal.

Today she has been drinking a lot and walking a lot slower again, standing like she's in pain, her legs just look odd, like she is really unsteady. She'll lie flat out and often outside in the rain but I don't like leaving her there. I put her on the sofa and after a while she leaped up to bark at the door. Once she had ran to the door she collapsed and I held her underneath but she couldn't hold her head up, she was really dizzy and disorientated and fell back against the wall. I have never seen her like this and found it very alarming. I have put her back on the sofa next to me to keep an eye, she is sleeping.

Do we take her to the vets? I don't want to stress her further if this could be something little, I think I am also afraid of what it could be given her age.

I would really appreciate any advice, I am so worried about her.

Thank you.