How to get back to normal speed after accelerating?

Hi! I have simple problem with speed changing. I want to increase velocity instantly after pushing and holding space bar and then when release key I want to get back to normal speed. Here is my code:

public class PlayerController : MonoBehaviour
{

    public GameObject focalPoint;
    private Rigidbody rb;
    public float force;
    ForceMode fm;
    float playerInput;
   
    void Start()
    {
        rb = GetComponent<Rigidbody>();
    }

    void Update()
    {
        playerInput = Input.GetAxis("Vertical");
      
        IncreaseSpeedDuringHoldingKey();
   
        print((int)rb.velocity.magnitude);// info about actual speed of GameObject
    }

    private void FixedUpdate()
    {
        rb.AddForce(playerInput * focalPoint.transform.forward * force * Time.deltaTime, fm);
    }

    void IncreaseSpeedDuringHoldingKey()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            fm = ForceMode.VelocityChange;
            force = 30f;
        }

        else if (Input.GetKeyUp(KeyCode.Space))
        {
            rb.velocity = transform.forward;
            fm = ForceMode.Force;
            force = 300F;   
        }
    }

}

As you can see I’ve tried with changing the velocity to rb.velocity = transform.forward but I’m dissatisfied with this solution because it stops my GameObject completely (rb.velocity.magnitude equals then to 0). What I want to do is to come back to normal speed instantly as if the rapid acceleration never happened (i.e. getting the speed from rb.AddForce(playerInput * focalPoint.transform.forward * force * Time.deltaTime, fm);).

Hey,
maybe you could safe the speed before boosting in a variable.
And after the boost is done, you set the velocity to the saved value?

Thanks for your answer! I must say before I asked this question I spent a few hours to solve this problem and nothing worked. Mostly because I couldn’t set the rb.velocity to boost (or slow down) into desirable direction. By that I mean when I added into my code this: rb.velocity = transform.forward * 30; my GameObject after pressing space bar moved into weird directions. But just moment ago I noticed that my mistake was in using transform.forward instead of focalPoint.transform.forward as is in the AddForce method. So I consider this problem as solved.