sleepy, lethargic, panting labrador

Question
Three days ago my boyfriend and I brought our 8 year old yellow lab to the beach.  Being that we live in Tennessee, my dog rarely gets these opportunities.  He played in the water three days in a row for approximately 30 each day.  I'm not sure if this is related to his current symptoms, but today he woke up feeling sick.  He was not interacting with us, nor did he show any interest in eating.  He threw up a thick yellow bile twice in a row then drank water and threw that up.  After this he started showing signs of being extremely tired yet restless.  His behavior was concerning enough to take him to the local emergency vet where they proceeded to do blood tests... returning with all normal results.  
We have returned from the vet's office and been back at our house for almost 8 hours.  My dog has shown no signs of improvement.  He remains restless in his attempts to sleep (non stop) and he has a constant pant.  He has not eaten and has only drank half a bowl of water in the past 16 hours.  
I dont know what to do and it is breaking my heart.

Answer
Hi Blythe,
Are you talking about the beach as in the ocean? Or a beach at a lake?
Panting is a sign of pain, anxiety, etc. Something somewhere is hurting and it could be his hips, his shoulders or even his leg joints, his heart. Blood tests won't indicate what hurts, but a hands on exam would have. Blood tests would indicate a heart issue if the right things were checked. Heartworm tests are important also.

You might want to call the vet and ask about starting him on some pain medications such as Duramaxx or any other type that the vet carries.

The reason I asked about a lake vs. the ocean is the presence of blue-green algae. It is blooming this time of year and can be fatal to dogs if they ingest even a small amount.
It blooms in lakes, ponds and stagnant waters. It isn't in the ocean as far as I know.

Another issue is this: is your dog on heartworm medication? If he isn't, then all that activity could have caused some issues with heartworms inside of his heart and he is having pain from that. This is a very serious matter. If he isn't on heartworm medication you need to have the vet check him again and do an xray or ultrasound of his chest.

He literally could be having a heart attack.
Those are all I can come up with Blythe. I truly hope it's just a strained muscle or back pain, but to be sure call your vet again and ask them about the above issues.
Please let me know how he does. I am quite concerned.