These last few weeks have been stressful, whether you're stuck at home or out there doing essential work, trying to stay safe. It takes a physical toll. You might be feeling stiff or achy. You might have a kink in your neck or a knot in your back. A hot bath can feel wonderful, but sometimes an ice pack will do more good. People often ask me which one is better.
As a general rule, I go with heat for tension and stiffness, and ice for sharp pain and inflammation.
In my experience, heat works best when you're feeling sore, achy or stiff. It relaxes the muscles and eases tension. You could take a hot bath or shower or use an electric heating pad, but you can also make a homemade heat pack with an old sock and some rice. My mom always kept a few of these around the house when I was a kid. Just fill an old sock with uncooked rice, tie or sew the end and heat it in the microwave. It works great. Of course, rice is a bit of a precious commodity right now. Any other grains or dried beans should work.
If you have inflammation, swelling, sharp pain or a new injury, you're much better off with ice. It reduces inflammation and dulls the sensation of pain. Heat can actually make inflammation worse. You should only apply ice for about 20 minutes at a time, but you can do it multiple times a day. If you don't have an ice pack, you can use a bag of frozen vegetables or ice cubes, or put a damp towel in a ziplock bag and stick it in the freezer. Whatever you use, wrap it up in a bit of cloth before putting it on your skin. If you don't like feeling cold, feel free to wrap the rest of your body in a warm blanket, sit by a fire or heater, make a cup of hot tea, and just ice the spot that hurts.
If you picked the right option, it should feel good. Or at least helpful. If heat or cold is making you feel worse, try the other one.
You can also alternate between the two, switching about every 20 minutes. I do this when something feels pinched or tweaked. I first tried it on the recommendation of an actor/chiropractor I was in a play with in my twenties. I tweaked something in my back and couldn't move without it hurting. He told me to take ibuprofen, elevate my legs, and alternate hot and cold every 20 minutes. It really helped. (I'm not necessarily recommending ibuprofen, ask your doctor, etc...)
This article gives a little more detail and a great chart for when ice or heat is called for.