My dog is not acting like her normal self?

My dog is a westie and she is currently 7 years old, going to be 8 in december. She used to love sleeping and loved going outside in the sun and just lying down. You could tell when she was happy by her eyes and just how she walks around. This week, she has been very sad, and i could tell by the way she walks and her eyes and just how she never barks. before this week,she was a big barker. Everytime she tries to bark, it looks to me like she cant. She walks right now, very slow. She wont eat as much as she did last week and she wont growl or bite anyone that picks her up when she doesnt want to be picked up, she used to do that before. I miss the old her, i dont know whats wrong. Her eyes are sagged and she walks like something is wrong. i know her well enough to know there is something wrong. I really want to know whats wrong. I dont know if this helps, but it is summer, where i live. Maybe she has been out in the sun for too long but i dont know. I really dont want to spend a lot of money at the vet because i dont know if she is reallly sick or is just sad. i think it might have to do with fireworks and thunder because this week there were fireworks a few nights ago and thunder a few days ago. But we usually get those 2 things a lot, so i dought she would get sad over that. Your thoughts and opinions will be greatly appriciated.. Please share what you know about this situation, im a nervous reck.