If you're a new dog parent and your dog is acting weird, you may be wondering, "what's wrong with my dog?" Even if you suspect something is wrong, you may not know how to tell if they are actually sick, what a sick dog looks or acts like, and why your pup's strange behavior may keep you up at night. And if your dog is actually sick and you don't notice the signs (or they're just good at hiding it), you may feel guilty and sad that you didn't know your dog was hurting.

While some symptoms of sickness, such as vomiting or diarrhea, can be obvious, many sickness behaviors in dogs are hard to pick up on if you don't know what to look for. Here are a few situations and signs that can help you figure out if your dog could be sick, and when you should consider contacting your veterinarian.

Sign #1: They're Not Eating

Most dogs will rarely miss a meal or special treat — especially when you set it in front of them. If your dog turns their nose up at their breakfast or dinner when they're normally gobbling it down, it's time to pay attention. Many things can cause a dog to stop eating. Nausea, tooth pain, anxiety, hormonal disorders, viral infections and gut pain are just a few of many things that can cause a dog to stop eating.

Schedule an appointment with your veterinarian if your dog doesn't eat for more than a day or misses more than two meals.

Sigh #2: They're Just Lying Around

If you notice that your dog is sleeping more, dragging behind on walks, uninterested in play or not playing as much as they used to, then something might be wrong. Sometimes, it's just too hot outside to play and exercise. When the temperatures rise, dogs are naturally a little more lazy. On the other hand, if it's not hot, then this behavior indicates that something more may be at play.

There are many things that can cause a loss of energy in a dog. Any kind of infection, whether it be viral, bacteria or fungal, can cause loss of energy. Heart disease or breathing problems of any kind can make a dog feel tired. Hormonal disorders, such as low thyroid, can cause increased lethargy. Obesity can cause a dog to sleep more because it is exhausting to get around. Obesity can also lead to things like degenerative joint disease making it more painful for your dog to run and play. This can create a frustrating cycle where your dog may struggle to exercise, gains more weight and exercises even less. . If your veterinarian suggests that your dog is obese, it is important to take their advice and work with them on a weight loss plan. Cancer, liver disease, kidney disease and neurological conditions such as seizures or canine cognitive dysfunction (otherwise known as doggie Alzheimer's disease) can also all make a dog act tired.

If your dog is getting up there in years, you might also think that they are moving less due to old age. While it is true that dogs slow down as they get older, it doesn't mean they should stop moving altogether. Senior dogs (those that are seven years and older) are still very capable of getting around and exercising.  If your older pup doesn't seem to play like they used to, it's probably worth a call to the veterinarian and have them checked , just to rule out any possible ailments. As your dog ages, your veterinarian will likely want to perform additional tests to ensure your pup stays in tip-top shape.

Pain can also masquerade as loss of energy. Gastrointestinal problems that cause a painful belly can make a dog act lethargic, and if a dog is in pain from arthritic joint disease, the pain may just manifest as sleeping more. The bottom line is that increased sleeping or laziness can definitely signal a problem. If it lasts for more than a day, call your vet. It's always better to be proactive and call your vet than wonder if your dog is sick for days.