If you often find yourself having nightmares and waking up in the middle of the night, join the club. Many people have similar problems. Either their nightmares wake them up too early or they wake up at the right time, but don't feel at all rested. For most people, those nightmares and related sleep problems are caused by general stress.
It's important to start by identifying your stress causes, if you want to sleep better. For example, do you have physical stress or mental/emotional stress? Maybe you have both. If you think you're being weighed down by your stress, don't worry. You can cut back on it.
Start by learning to let go of non-essential stress. For example, if your child left a toy in the living room, there's no reason to blow a mental fuse. If you have been spending more time at work than you need to or are paid for, cut down a bit. Also, no matter what, don't go to bed angry. You can't fix anything while you're asleep anyway. So, resolve issues before bed or table them for a later time.
Another thing you can do to limit stress before bed is start to implement a relaxation routine. Relaxation is different for each person. Some people like to take up yoga or meditation. Others just read a good book or drink a hot cup of tea. So, find what relaxes you and use it to chase those stress nightmares away. That way, you'll get a much more refreshing night of sleep.