There is a certain amount of pride that goes with the "pump" that lifters feel after a strong gym session. The tightness that might extend into the next day and the soreness for a lot of us is an indicator that we have done what we set out to do and are making gains.
There is one type of soreness that is never good though, and that is in your neck - which can be a sign of something that if it isn't already, could be a problem in the future for you and a person should be very careful to try to avoid this.
There are a number of reasons why this could be happening and you really should do all that you can in order to avoid it happening.
Most of your body can take a tremendous amount of punishment but your spine is an exception and really should be protected at all costs. If you are experiencing neck pain after or during a workout there are a couple of things that you could be doing wrong and you should correct them as soon as possible lest you end up with a chronic injury later in life.
Diving your head forward on lifts
This one is probably the most common and most people might not even be aware of it. For me it is just instinctual when I am trying to get those crucial last two reps in that sometimes I end up inadvertently tilting my head forward and then unintentionally putting undue strain on my neck.
You need to make a conscious effort to keep your spine and neck in line during lifts, even if they are not heavy lifts. This is easy enough to do considering the fact that nearly every gym in the world has the walls covered with mirrors. Many think this is a vanity thing but it is actually so you can check and correct your form. Form is much more important than how much you are lifting and is absolutely crucial to working out without injury. If your neck is pushing out during lifts, regardless of what the lift is, correct this immediately
Looking at yourself in odd angles
As helpful as the mirrors can be in proper form enforcement, it could actually be the reason why you end up putting your neck in a bad position. This is particularly true with deadlifts and any exercise facing downward on a bench where a person is trying to check their form by tweaking their neck.
I literally just said that the mirrors should be used to check form but this is not always the case and in many cases can be the reason why you end up putting your neck in a bad position. Here is the fix: If you are unsure about your form first do a set of something well below your max and check your form like that. Then you add the weights and make sure to keep your neck in the correct position. Also, working out with a friend comes in handy in these situations as they can check your form for you while you keep your neck in a straight position.
Holding your breath during lifts
I'm not sure why it is that people do this but a lot of people do. I know that I was guilty of it as well in the past. Proper breathing is important in order to prevent putting undue stress on certain parts of your body and when you are working out your body has a tremendous capability to do strange things if you put it under stress. While I do not know the specific reason WHY this tension ends up getting transferred to the neck if you don't breathe properly during lifts, it does seem to be the case. If you are breath holding lifter, you need to correct this or step down the weight as there is no benefit from holding your breath during lifts.
Lifting too much
This is a tough one to determine and even more difficult to correct. All of us gym junkies want to beat our personal bests and also chase higher numbers every time we are in the gym but if you are really struggling to bang out reps of 6 on something, there is a really good chance you are trying to do too much and need to step it back a bit. This might be disappointing to a lot of people out there but if you are overloading not only are you transferring the lift to other parts of the body that you don't want it to go to - such as your neck - you are probably damaging other parts of your body as well and also might not be using proper form - which is essential to gains without injury.
Lastly, you should never ignore certain aches and pains in the body and I feel that the lower back, the neck, or anything spinal should NEVER fall into the rather stupid cliche of "no pain, no gain." There are certain types of pain involved in lifting that is a sign that you are doing things right, but the spine is not one of them. You only get one spine buddy, and you need to protect it, even if this means stepping on the brakes a bit during lifts.
I have no qualifications for this advice other than what I have read, heard, and experienced in my own life. I lost 50 lbs and became the strongest I have been in my entire life after 10 years of basically ignoring my fitness. If I can do it, I believe many others out there an as well